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  • 1. Symmetrix Foundations, 1 Symmetrix Foundations EMC Global Education © 2004 EMC Corporation. All rights reserved. These materials may not be copied without EMCs written consent. 1Welcome to Symmetrix Foundations. EMC offers a full range of storage platforms, from the CLARiiON CX200 at thelow end to the unsurpassed DMX3000 at the high end. This training provides an architectural introduction to theSymmetrix family of products. The focus will be on DMX, but prior generations of Symmetrix will also be discussed.Copyright © 2004 EMC Corporation. All rights reserved.These materials may not be copied without EMCs written consent.EMC believes the information in this publication is accurate as of its publication date. The information is subject tochange without notice.THE INFORMATION IN THIS PUBLICATION IS PROVIDED “AS IS.” EMC CORPORATION MAKES NOREPRESENTATIONS OR WARRANTIES OF ANY KIND WITH RESPECT TO THE INFORMATION IN THISPUBLICATION, AND SPECIFICALLY DISCLAIMS IMPLIED WARRANTIES OF MERCHANTABILITY ORFITNESS FOR A PARTICULAR PURPOSE.Use, copying, and distribution of any EMC software described in this publication requires an applicable softwarelicense. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 2. Symmetrix Foundations, 2 Audio Portion of this Course The AUDIO portion of this course is supplemental to the material and is not a replacement for the student notes accompanying this course. EMC recommends downloading the Student Resource Guide (from the Supporting Materials tab) and reading the notes in their entirety. EMC Global Education © 2004 EMC Corporation. All rights reserved. 2The AUDIO portion of this course is supplemental to the material and is not a replacement for the student notesaccompanying this course.EMC recommends downloading the Student Resource Guide from the Supporting Materials tab, and reading the notesin their entirety. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 3. Symmetrix Foundations, 3 EMC Technology Foundations EMC Technology Foundations (ETF) is a curriculum that presents overviews of EMC products and technologies including: – Symmetrix and CLARiiON Storage Platforms and Software – SAN, NAS and CAS Networked Storage Solutions – Advanced storage management software The EMC Technology portfolio consists of end-to-end services and platforms designed to accelerate the implementation of Information Lifecycle Management (ILM) ILM uses EMC technologies to enable organizations to better, and more cost-effectively, manage and protect their data, and achieve regulatory compliance. It improves the availability of their business information in a way that connects its use to business goals and service levels This course represents one part of the ETF curriculum EMC Global Education © 2004 EMC Corporation. All rights reserved. 3Companies across all industries are constantly launching new business-critical applications turning information intostrategic corporate assets. Value to the bottom line for customers, suppliers, and partners is often directly related tohow easily this information can be shared across the enterprise and beyond.Information Lifecycle Management (ILM) is a flexible information-centric strategy that includes automating theprocess of connecting applications and servers in an organization to its company’s information. ILM includes DirectAttached Storage (DAS), Storage Area Network (SAN), Network Attached Storage (NAS), Content AddressedStorage (CAS), and software for management and automated provisioning.ILM facilitates the integration of SAN and NAS, extends the reach of enterprise storage, and delivers a common wayto manage, share, and protect information. It also takes advantage of today’s network and channel technologies toconsolidate servers and storage, centralize backup, and manage the explosive growth of data. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 4. Symmetrix Foundations, 4 Symmetrix Foundations After completing this course, you will be able to: Describe the basic architecture of a Symmetrix Integrated Cached Disk Array (ICDA) Identify the front-end, back-end, cache, and physical drive configurations of various Symmetrix models Explain how Symmetrix functionally handles I/O requests from the host environment Illustrate the relationship between Symmetrix physical disk drives and Symmetrix Logical Volumes Identify the media protection options available on the Symmetrix EMC Global Education © 2004 EMC Corporation. All rights reserved. 4These are the learning objectives for this training. Please take a moment to read them. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 5. Symmetrix Foundations, 5 Symmetrix Integrated Cached Disk Array Highest level of performance and availability in the industry Consolidation – Capacities to Terabytes – Vast host connectivity – SAN or NAS Advanced functionality – Parallel processing architecture Enginuity Operating – Intelligent prefetch Environment – Auto cache destage – Base services for data – Dynamic mirror service policy integrity, optimization, security, and Quality of – Multi-region internal memory Service – Predictive failure analysis and call home – Core services for data mobility, sharing, repurposing, – Back-end optimization and recovery EMC Global Education © 2004 EMC Corporation. All rights reserved. 5There are basically three categories of storage architectures: Cache Centric, Storage Processor centric, and JBOD (Justa Bunch Of Disks). The Symmetrix falls under the category of cache centric storage and is an Integrated Caching DiskArray. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 6. Symmetrix Foundations, 6 Enginuity Operating Environment Enginuity Operating Environment is the Symmetrix software that: Symmetrix Based Applications – Manages all operations Host Based Management Software – Ensures data integrity ISV Software – Optimizes performance Enginuity is often referred to as “the microcode” Solutions Enabler Management Solutions Enabler provides common API and CLI interface for managing Enginuity Operating Environment Symmetrix and the entire storage infrastructure EMC and ISV develop Symmetrix Hardware management software supporting heterogeneous platforms using Solutions Enabler API and CLIs EMC Global Education © 2004 EMC Corporation. All rights reserved. 6Before we get into the hardware, let’s briefly introduce the software components, as most functionality is based insoftware and supported by the hardware.Enginuity is the operating environment for the Symmetrix storage systems. Enginuity manages all Symmetrixoperations, from monitoring and optimizing internal data flow, to ensuring the fastest response to the user’s requestsfor information, to protecting and replicating data. Enginuity is often referred to as “the Microcode”.Solutions Enabler is storage management that provides a common access mechanism for managing multivendorenvironments, including the Symmetrix, storage, switches, and host storage resources. It enables the creation ofpowerful storage management applications that don’t have to understand the management details of each piece withinan EMC user’s environment.Solutions Enabler is a development initiative (that is, a program available to Integrated Software Vendors (ISVs) anddevelopers through the EMC Developers Program™) and provides a set of storage application programming interfaces(APIs) that shield the management applications from the details beneath. It provides a common set of interfaces tomanage all aspects of storage. With Solutions Enabler providing building blocks for integrating layered softwareapplications, ISVs and third-party software developers (through the EMC Developers Program), and EMC softwaredevelopers are given wide-scale access to Enginuity functionality. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 7. Symmetrix Foundations, 7 Symmetrix Card Cage DMX800 DMX1000 DMX2000 DMX3000 Model Maximum Maximum Maximum Maximum Maximum Disk Front End Back End Cache Cache Drives Directors Directors Directors DMX800 2 2 2 64GB 120 DMX1000 6 2 4 128GB 144 DMX1000P 4 4 4 128GB 144 DMX2000 12 4 8 256GB 288 DMX2000P 8 8 8 256GB 288 DMX 3000 8 8 8 256GB 576 8830 8 8 4 64GB 384 8530 4 4 4 64GB 96 8230 2 2 2 32GB 48 EMC Global Education © 2004 EMC Corporation. All rights reserved. 7Though we logically divide the architecture of the Symmetrix into Front End, Back End, and Shared Global Memory,physically, these director and memory cards reside side-by-side within the card cage of the Symmetrix. The DMX “P”model is configured for maximum performance rather than connectivity. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 8. Symmetrix Foundations, 8 DMX2000 EMC Global Education © 2004 EMC Corporation. All rights reserved. 8Symmetrix Architecture is based on the concept of N + 1 redundancy (one more component than is necessary foroperation).Continuous Operation even if failures occur to any major component: • Global Memory Director boards • Environmental Control Card • Channel Director boards • Cooling Fan Modules • Disk Director boards • Power modules • Disk drives • Batteries • Communications Control Card • Service ProcessorPower Subsystem: The Symmetrix has a modular power subsystem featuring a redundant architecture that facilitatesfield replacement without interruption. The Symmetrix power subsystem connects to two dedicated or isolated ACpower lines. If AC power fails on one AC line, the power subsystem automatically switches to the other AC line.System Battery Backup: The Symmetrix backup battery subsystem maintains power to the entire system if AC poweris lost. The backup battery subsystem allows Symmetrix to remain online to the host system for one to three minutes(set in IMPL.bin file) in the event of an AC power loss, allowing the directors to flush cache write data to the diskdevices. Symmetrix continually recharges the battery subsystem whenever it is under AC power. When a power failureoccurs, power switches immediately to the backup battery, and Symmetrix continues to operate normally. When thebattery timer window elapses, Symmetrix presents a busy status to prevent the attached hosts from initiating any newI/O. The Symmetrix destages any write data still in cache to disk, spins down the disk devices, and retracts the headsand powers down.Symmetrix Emergency Power Off: The Symmetrix emergency power off sequence allows 20 seconds to destagepending write data. When the EPO switch is set to off, Symmetrix immediately switches to battery backup, andinitiates writes of cache data. Data is written to the first available spare area on any devices available for write. Thedirector records that there are pending write operations to complete, and stores the location of all data that has beentemporarily redirected. When power is restored, all data is written to its proper volumes. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 9. Symmetrix Foundations, 9 Cache Management Data path through Symmetrix Data destaged from cache EMC Global Education © 2004 EMC Corporation. All rights reserved. 9There are three functional areas: • Global Memory - provides cache memory and link between independent front end and back end • Channel director - how the Symmetrix connects to the host (server) environment (multi-processor circuit boards) • Disk director- how the Symmetrix controls and manages its physical disk drives, referred to as Disk Directors or Disk AdaptersChannel directors handle I/O request from the host, while disk directors manage access to disk drives. The channeldirectors and disk directors share global memory. Cache is used for staging and destaging data between the host andthe disk drives. Data is stored in cache as write pending, and an acknowledgement of data receipt is returned to thehost. The disk directors will write the data from cache to disk at a later time. The cache directory contains informationon data location, which data is still in cache, and which data has been written to disk. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 10. Symmetrix Foundations, 10 Direct Matrix Architecture EMC Global Education © 2004 EMC Corporation. All rights reserved. 10What differentiates the Symmetrix generations and models is the number, type, and speed of the variousprocessors, and the technology used to interconnect the front-end and back-end with cache.The DMX Series system currently uses M5 memory boards. Each memory board has sixteen ports, one to eachdirector. Each region can sustain a data rate of 500MBs, 4 regions per card, so 2GB per card. If a director isremoved from a system, the usable bandwidth is not reduced. If a memory board is removed, the usable bandwidthis dropped by 2GB/s. In addition to 8 ports to front end hosts, or backend disks (depending on board type), eachdirector also has 8 ports to memory, one to each of the memory boards. All four processors can connectconcurrently to four different memory boards. In a fully configured Symmetrix DMX2000/3000 system, each ofthe eight director ports on the sixteen directors connects to one of the sixteen memory ports on each of the eightglobal memory directors. These 128 individual point-to-point connections facilitate up to 128 concurrent globalmemory operations in the system. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 11. Symmetrix Foundations, 11 Symmetrix DMX Architecture Servers Separate Control and Communications Message Matrix Disks EMC Global Education © 2004 EMC Corporation. All rights reserved. 11Another major performance improvement with the DMX is the separate control and communications matrix thatenables communication between the directors, without consuming cache bandwidth. This becomes more apparent aswe talk about read and write operations and the information flow through the Symmetrix later in this training. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 12. Symmetrix Foundations, 12 DMX Director Pairing EMC Global Education © 2004 EMC Corporation. All rights reserved. 12Directors are paired Processor to Processor using the 17 rule. This means mirrors will not be placed across Directorsusing the 17 rule (unless only 2 Directors are present). Paired directors provide redundant paths to dual ported disks,and will not use the same Port Bypass Card (PBC) in order to maintain redundancy on the Port Bypass Card level. ThePBC acts as the hub for all the Fibre disk drives in the disk cage. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 13. Symmetrix Foundations, 13 DMX: Dual-ported Disk and Redundant Directors Disk Director 1 Disk Director 16 Directors are always configured in pairs to facilitate secondary paths S to drives P Each disk module has two fully P independent Fibre Channel ports S Drive port connects to the Director S by a separate loop – Each port connects to different P P Directors in the Director pair – Port bypass cards prevent a S Director failure or replacement S from affecting the other drives on the loop P P Directors have four primary loops for normal drive communication S S and four secondary loops to provide alternate path if the other P director fails (based on P performance models) S P = Primary Connection to Drive S= Secondary Connection for Redundancy EMC Global Education © 2004 EMC Corporation. All rights reserved. 13Symmetrix DMX back-end employs an arbitrated loop design and dual-ported disk drives. Here is an example of a9 disk per loop configuration. Each drive connects to two Disk Directors through separate Fibre Channel loops. Theloops are configured in a star-hub topology with gated hub ports and bypass switches, that allow individual FibreChannel disk drives to be dynamically inserted or removed. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 14. Symmetrix Foundations, 14 Back-end Director Pairing 9-drive loop Director 1d PBC d A A B A c A B B B b A A 16d 1d 16d 1d 16d 1d 16d 1d 16d B A C0 C1 C2 C3 C4 C5 C6 C7 C8 a A B Director 16d B B A A d A B PBC B A c B B Legend A A b A B Primary Connection Director 1d B A a Bypass Connection Director 1d B B Primary Connection Director 16d Bypass Connection Director 16d EMC Global Education © 2004 EMC Corporation. All rights reserved. 14The Port Bypass Card contains the switch elements and control functions to allow intelligent management of the twoFC-AL loops embedded in each disk cage midplane. There are two Port Bypass Cards per disk cage midplane. Eachdisk cage midplane can support 36 FC drives.Each Processor has two ports, each with devices in the Front, as well as in the Back, Disk Midplane. In the above slide,we are showing only one port from Director 1d, and one port from Director 16d. Notice that each Director has thepotential to access all Drives in the loop (9-drive loop configuration in this example). Notice also that using the PortBypass Card, each director is currently accessing only a portion of the drives (Director 1d has 4 Drives; Director 16dhas 5 Drives).These Directors will have an opposite configuration on their second port, which is connected to a different Port BypassCard and Disk Midplane. For example, Director 1d has 4 Drives in this Disk Midplane, and on its other port it willhave 5. Director 16d has 5 Drives in this Disk Midplane, and on its other port it will have 4. Director 1d and Director16d will be paired in both the front and back Disk Midplanes (only one shown here). With no component failure, eachprocessor will manage 4 drives on one port and 5 Drives on the other. These reside in Front and Back Disk Midplanesand are referred to as C and D Devices. If the processor on Director 1d fails, the processor on Director 16d will nowaccess all 9 Drives on this loop. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 15. Symmetrix Foundations, 15 DMX800 Architectural Overview SPE Enclosure EMC Global Education © 2004 EMC Corporation. All rights reserved. 15The physical layout of the DMX800 is very different than previous Symmetrix models. Directors, Memory, backadapter functionality, communications and environmental functions are all in the Storage Processor Enclosure(SPE). The DMX800 looks similar to the CLARiiON CX600 series and does in fact use the same back end stylecomponents.The SPE Contains 2 - 4 Fibre director boards, up to 2 Multi Protocol Boards, 2 Memory boards, 2 Front-end Back-end (FEBE) adapters, Redundant Power Supplies and Fan module.The DMX800 does not contain disk drive cages; drives are in a separate Disk Array Enclosure (DAE). Each DAEhas 2 Link Controller Cards (LCCs) and 2 Power Supplies. The Service Processor is replaced by a 1U (1U = 1.75”)Server, the Server will support 4 SPEs via 4 of its 6 Ethernet connections.Batteries, or Standby Power Supplies (SPS), are in a separate 1U enclosure. Each SPS enclosure contains twoSPSes, and supports either two DAEs or one SPE. There are no ECM or CCM boards in the DMX800. TheCommunication and Environmental functions are taken care of by Directors and FEBE Adapters. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 16. Symmetrix Foundations, 16 Symmetrix 5.X LVD Architecture 3 Bay Cabinet 8830 1 Bay 8530 Cabinet Front End Shared Global Memory Back End ½ Bay 8230 Top High Top Low Cabinet Channel Director Disk Director Processor b Processor b PowerPC 750 PowerPC 750 333Mhz 333Mhz 400 MBS 400 MBS Internal Cache Internal Bus Bus Processor a Processor a PowerPC 750 PowerPC 750 333 Mhz 333 Mhz High Memory Low Memory 80 MBS SCSI LVD Bus Bottom Low Bottom High EMC Global Education © 2004 EMC Corporation. All rights reserved. 16Here is another example of the MOSAIC 2000 Architecture. This is the basic architecture for Symmetrix 5.X LVD: • Bus speed of 400MB/s for an aggregate of 1600 MB/s • Back End Directors and Drives support Ultra 2 SCSI LVD (Low Voltage Differential) and the bus speed of 80 MB/s • The director processors are now 333 Mhz; ESCON directors are 400 Mhz • Each director connects to 2 internal system buses (Top High & Bottom Low for odd directors | Bottom High & Top Low for even directors ) • M4 Generation of Memory Boards support LVD ( Low Voltage Differential or Ultra 2 SCSI Enginuity 5567 or greater)The Symmetrix 5 (8730, 8430) follows the same bus structure but has speeds of 360MB/s for an aggregate of 1440MB/s.The Symmetrix 4.X family is based on a dual system bus design. Each director is connected to either the X bus (oddnumbered director) or Y bus (even numbered director). Each director card has two sides, the b processor (top half)and the a processor (bottom half). Data is transferred throughout the Symmetrix (from Channel Director to Memory toDisk Director) in a serial fashion along the system buses. For every 64 bits of data, the Symmetrix creates a 72 bit“Memory Word” (64 bits of data + 8 bits of parity). These Memory Words are then sent in a serial fashion across theinternal buses to director from cache or to cache from director. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 17. Symmetrix Foundations, 17 Symm 5: Dual-Initiator Disk Director Disk Directors are installed in pairs to facilitate secondary DA 1 MIDPLANE paths to drives In the unlikely event of a disk Port C director processor failure, the Processor b adjacent director will continue servicing the attached drives through secondary path Port D – In this example, DA1 processor “b” would see ports C & D for DA2 processor “b” DA 2 as its A & B ports in a fail-over scenario Port C Protecting against DA Processor b processor card failure Port D Physical drives are not dual- MIDPLANE ported but are connected via a dual-initiator SCSI Bus Solid line = Primary Path Volumes are typically mirrored Dotted line = Secondary Path across directors EMC Global Education © 2004 EMC Corporation. All rights reserved. 17Symmetrix 4 and 5 architectures utilize a dual-initiator back-end architecture that ensures continuous availability ofdata in the unlikely event of a Disk Director failure. This feature works by having two disk directors shadow thefunction of each other. That is, each disk director has the capability of servicing any or all of the disk devices of thedisk director it is paired with. Under normal conditions, each disk director only services its disk devices. If Symmetrixdetects a disk director hardware failure, Symmetrix “calls home” but continues to read from or write to the diskdevices through the disk director it is paired with. When the source of the failure is corrected, Symmetrix returns theI/O servicing of the two disk directors to their normal state.Prior to the Symmetrix DMX, mirrored volumes were configured with what is known as the “rule of 17”. Because ofwhere within the card cage the DA pairs reside (1/2, 3/4, 13/14, 15/16), as long as the sum of the DA director numbersequals 17 (1/16, 2/15, 3/14, 4/13), the mirrors will always be on different internal system buses and dual initiators forthe highest availability and maximum Symmetrix resources.Note: On the 4.x family, dual-initiation occurs by physically connecting one disk director’s port card to the port card ofthe adjacent disk director with a dual slotted adapter card. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 18. Symmetrix Foundations, 18 Symmetrix Back End Disk Director Port C Processor b Port D Symmetrix 4 and 5 architectures use 40/80MB/s Port C SCSI to connect physical drives with a maximum of 12 Processor a Port D drives per port DAs installed in pairs on adjacent slots within the card A A cage of Symmetrix d B A DMX Architecture uses 2Gb A B c B Fibre Channel drives B – Eight ports per Director A A – Maximum 18 dual ported b B A drives per port A B a B B EMC Global Education © 2004 EMC Corporation. All rights reserved. 18The primary purpose of the Back End director is to read and write data to the physical disks. However, when it is notstaging data in cache or destaging data to disk, the disk director is responsible for proactive monitoring of physicaldrives and cache memory. This is referred to as disk and cache “scrubbing”.“Disk Scrubbing” or Disk Error Correction and Error Verification: The disk directors use idle time to read data andcheck the polynomial correction bits for validity. If a disk read error occurs, the disk director reads all data on thattrack to Symmetrix cache memory. The disk director writes several worst case patterns to that track searching formedia errors. When the test completes, the disk director rewrites the data from cache to the disk device, verifying thewrite operation. The disk microprocessor maps around any bad block (or blocks) detected during the worst case writeoperation, thus skipping defects in the media. When the internal soft error threshold is reached, the Symmetrix serviceprocessor automatically dials the EMC Customer Support Center and notifies the host system of errors via sense data.“Cache Scrubbing” or Cache Error Correction and Error Verification: The disk directors use idle time to periodicallyread cache, correct errors, and write the corrected data back to cache. This process is called “error verification orscrubbing.” When the directors detect an uncorrectable error in cache, Symmetrix reads the data from disk and takesthe defective cache memory block offline until an EMC Customer Engineer can repair it. Error verification maximizesdata availability by significantly reducing the probability of encountering an uncorrectable error by preventing biterrors from accumulating in cache. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 19. Symmetrix Foundations, 19 Symmetrix Global Cache Directors Memory boards are now referred to as Global Cache Directors and contain global shared memory Boards are comprised of memory chips and divided into four addressable regions Symmetrix has a minimum of 2 memory boards and a maximum of 8. Generally installed in pairs Individual cache directors are available in 2 GB, 4 GB, 8 GB, 16 GB and 32 GB sizes Memory boards are FRUs and “hot swappable” (does not require Symmetrix power down or “reboot”) EMC Global Education © 2004 EMC Corporation. All rights reserved. 19Cache boards are designed for each family of Symmetrix. Symmetrix 4.8 uses the M2 generation of memory boardsthat connect to both the X and Y internal buses. Symmetrix 5 uses the M3/M4 generation of memory boards and theDMX uses M5. Because these boards have different designs, they cannot be swapped between families of Symmetrix.On Symmetrix 5, memory boards that connect to the Top High and Bottom High internal system buses are referred toas “High Memory”. Conversely, boards that connect to Top Low and Bottom Low are known as “Low Memory”.DMX uses direct connections between directors and cache.When configuring cache for the Symmetrix DMX systems, follow these guidelines: • A minimum of four and a maximum of eight cache director boards is required for the DMX2000 and DMX3000 system configuration; and a minimum of two and a maximum of four cache director boards is required for the DMX1000 system configuration. • Two-board cache director configurations require boards of equal size. • Cache directors can be added one at a time to configurations of two boards and greater. • A maximum of two different cache director sizes is supported, and the smallest cache director must be at least one-half the size of the largest cache director. • In cache director configurations with more than two boards, no more than one half of the boards can be smaller than the largest cache director. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 20. Symmetrix Foundations, 20 Cache Age Link Chain Locality of Reference – If a data block has been recently used, adjacent data will be needed soon – Prefetch algorithm detects sequential data access patterns Data Re-use – Accessed Data will probably be used again Least Recently Used – Flush old data from cache and only keep active data in cache – Free up cache slots that are inactive to make room for more active data EMC Global Education © 2004 EMC Corporation. All rights reserved. 20Cache is allocated in tracks referred to as cache slots, which are 32Kbytes in size (57 Kbytes for Mainframe). If theSymmetrix is supporting both FBA and CKD emulation within the same frame, the cache slots will equal the largesttrack size, 57K (3390). The Track Table is a directory of the data residing in cache and of the location/condition of thedata residing on Symmetrix physical disk(s). Track Tables are used to keep the status of each track, and of each logicalvolume. Approximately 16 Bytes of cache space is used for each track.Prefetching is done by the Disk Director. Once sequential access is detected, prefetch is automatically turned on forthat logical volume. Prefetch is initiated by 2 sequential accesses to a volume. Once turned on, for every sequentialaccess, the Symmetrix will pull the next two successive tracks into cache (access to track 1 on cylinder 1 and willprompt the prefetch of tracks 2 & 3 on cylinder 1). After 100 sequential accesses to that volume, the next sequentialaccess will initiate the prefetching of the next 5 tracks on that volume (access to track 1 on cylinder 10 will prompt theprefetch of tracks 2, 3, 4, 5 & 6 on cylinder 10). After the next 100 sequential accesses to that volume, the prefetchtrack value is increased to 8 (access to track 1 on cylinder 100 will prompt the prefetch of tracks 2, 3, 4, 5, 6, 7, 8 & 9on cylinder 100). Any non-sequential accesses to that volume will turn the prefetch capability off.As data is placed into cache or accessed within cache, it is given a pseudo timestamp. This allows the Symmetrix tomaintain only the most frequently accessed data in cache memory. The data residing in cache is ordered through anAge-Link-Chain. As data is touched (read operation for example), it moves to the top of the Age-Link-Chain. Everytime a director performs a cache operation, it must take control of the LRU algorithm. This forces the director to markthe least recently used data in cache to be overwritten by the next cache operation. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 21. Symmetrix Foundations, 21 Read Operations EMC Global Education © 2004 EMC Corporation. All rights reserved. 21Read HitIn a read hit operation, the requested data resides in global memory. The channel director transfers the requested datathrough the channel interface to the host, and updates the global memory director. Since the data is in global memory,there are no mechanical delays due to seek, latency, and rotational position sensing that is encountered with disk.Read MissIn a read miss operation, the requested data is not in global memory, and must be retrieved from a disk device. Thedisk director stores the data in global memory and updates the directory table. The Channel director then reconnectswith the host and transfers the data. The host sends an acknowledgement and the directory tables are updated. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 22. Symmetrix Foundations, 22 Write Operations EMC Global Education © 2004 EMC Corporation. All rights reserved. 22Fast WriteOn a write command, the channel director places the incoming blocks directly into global memory. The channeldirector sends an acknowledgement to the host. The directory tables are updated, and the disk director willasynchronously destage the data from global memory to the disk device.Delayed fast WriteA delayed fast write occurs only when the fast write threshold has been exceeded. That is, the percentage of globalmemory containing modified data is higher than the fast write threshold. If this situation occurs, the Symmetrix systemdisconnects the channel director(s) from the channel. The disk directors then destage the Least Recently Used data todisk. When sufficient global memory space is available, the channel directors reconnect to their channels, and processthe host I/O request as a fast write. The Symmetrix system continues to process read operations during delayed fastwrites. With sufficient global memory present, this type of global memory operation rarely occurs. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 23. Symmetrix Foundations, 23 Cache Allocation Cache algorithms are designed to optimize cache utilization and “fairness” for all Symmetrix Volumes Cache allocation dynamically adjust based on current usage – Symmetrix constantly monitors system utilization (including individual volume activity) – “More active” volumes are dynamically allocated additional cache resources from relatively “less active” volumes – Each volume has a minimum and maximum number of cache slots for write operations EMC Global Education © 2004 EMC Corporation. All rights reserved. 23When a Symmetrix is IMPL’ed (Initial Microcode Program Load), the amount of available cache resources isautomatically distributed to all of the logical volumes in the configuration. For example, if a Symmetrix wereconfigured with 100 logical volumes of the same size and emulation, then at IMPL, each one would receive 1% ofavailable cache resources. As soon as reads and writes to volumes begins, the Symmetrix Operating Environment(Enginuity) dynamically adjusts the allocation of cache. If only 1 of the 100 volumes was active, it would getincrementally more cache and the remaining amount would be redistributed to the other 99 volumes. Managing eachindividual volume’s write activity enables Enginuity to typically prevent system-wide delayed write situations. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 24. Symmetrix Foundations, 24 Enginuity Overview Operating Environment for Symmetrix – Each processor in each director is loaded with Enginuity • Downloaded from service processor to directors over internal LAN • Zipped code loaded from EEPROM to SDRAM (control store of director) – Enginuity is what allows the independent director processors to act as one Integrated Cached Disk Array • Also provides the framework for advanced functionality like SRDF, TimeFinder,...etc. – All DMX ship with the latest Enginuity 5670.73.69 Symmetrix Hardware Field Release Level of Microcode Field Release Level of Service Processor Supported: ‘Family’ Symmetrix Microcode Code 50 = Symm3 (Major Release (Minor Release Level) (Minor Release Level) 52 = Symm4 Level) 55 = Symm5 56 = DMX EMC Global Education © 2004 EMC Corporation. All rights reserved. 24Non-disruptive microcode upgrade and load capabilities are currently available for the Symmetrix. Symmetrix takesadvantage of a multi-processing and redundant architecture to allow for hot loadability of similar microcode platforms.The new microcode loads into the EEPROM areas within the channel and disk directors, and remains idle untilrequested for hot load in control storage. The Symmetrix system does not require manual intervention on thecustomer’s part to perform this function. All channel and disk directors remain in an on-line state to the host processor,thus maintaining application access. Symmetrix will load executable code at selected “windows of opportunity” withineach director hardware resource, until all directors have been loaded. Once the executable code is loaded, internalprocessing is synchronized and the new code becomes operational. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 25. Symmetrix Foundations, 25 5670+ Management Features Enhancements 5670+ Management Features – End User Configuration • User control of volumes and type – Symm Purge • Secure deletion method – Logical Volumes • Increased number of “hypers” – Volume Expansion • Striped meta expansion EMC Global Education © 2004 EMC Corporation. All rights reserved. 25User Configuration - Enginuity v 5670+ will allow users to un-map CKD volumes, delete CKD volumes, or convertCKD volumes to FBA. These user configuration controls will simplify the task of reusing a Symmetrix by notrequiring an EMC resource to modify the “bin” file.Symm Purge - provides customers a secure method of deleting (electronic shredding) sensitive data. This willsimplify the reuse of drive assets.Logical Volumes - v 5670+ will support an increased number of hypers per spindle. The number of hypers willdepend on the protection scheme.Volume Expansion - Previous microcode versions only supported the expansion of concatenated meta volumes.V5670+ will now support the expansion of both striped and concatenated meta volumes. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 26. Symmetrix Foundations, 26 5670+ Business Continuity Features 5670+ Business Continuity Features – SRDF/A • multi-session support – Protected Restore • Enhanced restore features – SNAP Persistence • Preserves snap session EMC Global Education © 2004 EMC Corporation. All rights reserved. 26SRDF/A- currently (v 5670) SRDF-A can only support a single-session. With v5670+ code, support will be availablefor multi-session SRDF/A data replication. Multi-session uses host control (Mainframe only). Cycle switching issynchronized between the single-session SRDF/A Symmetrix pairs.Protected Restore- v 5670+ provides Protected Restore features. While the restore is in progress, read miss data willcome from the BCV, writes to the Standard volume will not propagate to the BCV, and the original Standard to BCVrelationship will be maintained.SNAP Persistence - v 5670+allows a protected snap restore and preserves the virtual snap session when the restoreterminates. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 27. Symmetrix Foundations, 27 Configuration Considerations Understand the applications on the host connected to the Symmetrix system – Capacity requirements – I/O rates – Read/Write ratios – Read/Write - Sequential or Random Understand special host considerations – Maximum drive and file system sizes supported – Consider Logical Volume Manager (LVM) on the host and the use of data striping – Device sharing requirements - Clustering Determine Volume size and appropriate level of protection – Symmetrix provides flexibility for different sizes and protection within a system – Standard sizes make it easier to manage Determine connectivity requirements – Number of channels available from each host Distribute workloads from the busiest to the least busy EMC Global Education © 2004 EMC Corporation. All rights reserved. 27The best possible performance will only be achieved if all the resources within the system are being equally utilized.This is much easier said than done, but through careful planning, you will have a better chance for success. Planningstarts with understanding the host and application requirements. Within the Symmetrix bin-file, the emulation type,size in cylinders, count, number of mirrors, and special flags (like BCV, DRV, Dynamic Spare) are defined. EachSymmetrix Logical Volume is assigned a hexadecimal identifier. The bin file also tells the Channel director whichvolumes are presented on which port, and the address used to access it. From the Host’s perspective, when a devicediscovery process occurs, the information provided back to the OS appears to be referencing a series of SCSI diskdrives. To an Open Systems host, the Symmetrix looks like a JBOD (Just a Bunch Of Disks). The host is unaware ofthe bin file, RAID protection, remote mirroring, BCV mirrors, dynamic sparing, ...etc. In other words, the host “thinksit’s getting” an entire physical drive. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 28. Symmetrix Foundations, 28 Symmetrix Configuration Information Symmetrix configuration information Bin file stored in two places includes the following: – Physical hardware that is installed – number and type of directors, memory, and physical drives – Mapping of physical disks to logical volumes – Mapping of addresses to volumes and to front-end directors – Operational parameters for front-end directors Configuration information is referred to as the IMPL.bin file or simply “the bin file” Stored in two places: – On the Hard Disk of the Symmetrix Service Processor – In the EEPROM of each Symmetrix Director Directors Service Processor Configuration changes can also be made using EMC ControlCenter Configuration Manager GUI and Solutions Enabler CLI EMC Global Education © 2004 EMC Corporation. All rights reserved. 28Two very important concepts:Each director (both Channel and Disk) has a local copy (stored in EPROM) of the configuration file. This enablesChannel Directors to be aware of the Disk Directors that are managing the physical copy(ies) of Symmetrix LogicalVolumes and vice versa. The bin file also allows Channel Directors to map host requests to a channel address, ortarget and LUN to the Symmetrix Logical Volume.Changes made to the bin file (non-SDR changes) must first be made to the IMPL.BIN on the Service Processor andthen downloaded to the directors over the internal Ethernet LAN. Though Customer Service has the capability to doremote bin file updates (using the EMC Remote application), standard operating procedure mandates the CE bephysically present for all configuration changes. In addition, CS requires that all CEs do a comparison analysis priorto committing changes (the existing IMPL.BIN is compared to the proposed IMPL.BIN). Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 29. Symmetrix Foundations, 29 Disk Performance Basics Rotational Delay Three components of disk performance – Time to reposition actuator - Seek time – Rotational latency – Transfer rate With a Symmetrix, I/Os are serviced Position from cache not from the physical HDA Actuator – Minimizes the inherent latencies of physical disk I/O – Disk I/O at memory speeds Transfer Data Seek Disk I/O = + Rotational Delay + Transfer Rate time time EMC Global Education © 2004 EMC Corporation. All rights reserved. 29When you look at a physical disk drive, a read or write operation has three components that add up to the overallresponse time.Actuator positioning is the time it takes to move the read/write heads over the desired cylinder. This is mechanicalmovement and is typically measured in milliseconds. The actual time that it takes to reposition depends on how far theheads have to move, but this contributes to the greatest share of the overall response time.Rotational Delay is the time it takes for the desired information to come under the ready write head. This time is thefunction of the revolutions per second, or drive RPM. The faster the drive turns, the lower the rotational latency. A10,000 RPM drive has an average rotational latency of approximately 3.00 milliseconds, which is half the time it takesto make one revolution.Transfer Rate is the smallest time component and consists of the time it takes to actually read/write the data. This is afunction of drive RPM and the data density. It is often measured as internal transfer rate or external transfer rate. Theexternal rate is the speed that the drive transfers data to the controller. This is limited by the internal transfer rate, butwith buffers on the drive modules themselves, it allows faster transfer rates.The design objective of a Symmetrix is to not limit the performance of host applications based on the performancelimitations of the physical disk. This is accomplished using cache. Write operations are to cache and asynchronouslydestage to disk. Read operations are from cache using the Least Recently Used algorithm and prefetching to keep theinformation that is most likely to be accessed in memory. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 30. Symmetrix Foundations, 30 Symmetrix Disk Comparisons 36 GB 18 GB 36 GB 73 GB 146 GB 181 GB 73 GB 73 GB 146 GB Spindle 10,000 10,000 10,000 15,000 10,000 Speed 7,200 10,000 10,000 10,000 Symmetrix Sym 4.8 Sym 5.X Sym 5.X Sym 5.X Sym 5.X Sym 5.X DMX DMX DMX Architecture Interface Ultra SCSI Ultra SCSI Ultra SCSI Ultra SCSI Ultra SCSI Ultra SCSI Fibre Fibre Fibre Channel Channel Channel EMC Global Education © 2004 EMC Corporation. All rights reserved. 30Symmetrix physical drives are manufactured by our supplier (Seagate, Hitachi) to meet EMC’s rigorous qualitystandards and unique product specifications. These specification include, dedicated microprocessors (that can be XORcapable), the most functionally robust microcode available, and large onboard buffer memory (4MB – 32MB).Again, while the physical speed of disk drives does contribute to the overall performance, the Symmetrix design is formost read or write operations to be handled from cache. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 31. Symmetrix Foundations, 31 Mapping Physical Volumes to Logical Volumes Symmetrix Physical Drives are split into Hyper Volume Extensions Logical 4.2 GB Physical Volume Drive Logical 4.2 GB Volume 18 GB Logical 4.2 GB Volume Logical 4.2 GB Volume Hyper Volume Extensions (disk slices) are then defined as Symmetrix Logical Volumes – Symmetrix Logical Volumes are internally labeled with hexadecimal identifier (0000-FFFF) – Maximum number of Logical Volumes per Symmetrix configuration = 8192 EMC Global Education © 2004 EMC Corporation. All rights reserved. 31While “hyper -volume” and “split” refer to the same thing (a portion of a Symmetrix physical drive), a “logicalvolume” is a slightly different concept. A logical volume is the disk entity presented to a host via a Symmetrixchannel director port. As far as the host is concerned, the Symmetrix Logical Volume is a physical drive.Do not confuse Symmetrix Logical Volumes with host-based logical volumes. Symmetrix Logical Volumes aredefined by the Symmetrix Configuration (BIN File). From the Symmetrix perspective, physical disk drives are beingpartitioned into Hyper Volumes. A Hyper Volume could be used as an unprotected Symmetrix Logical Volume, amirror of a Symmetrix Logical Volume, a Business Continuance Volume (BCV), a parity volume for Parity RAID, aremote mirror using SRDF, a Disk Reallocation Volume (DRV), …etc. Host-based logical volumes are configured bycustomers through Logical Volume Manager software (Veritas LVM, NT Disk Administrator, ...etc.).Note: In actuality, the true useable capacity of the drive would be less than 18GB due to disk formatting and overhead(track tables, etc.). This would result in each of the 4 splits in this example being approximately 4.21GB in size (opensystems). Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 32. Symmetrix Foundations, 32 Symmetrix Logical Volume Specifications Physical Physical Physical Physical Physical Disk Disk Disk Disk Disk Volume Specifications vary with Enginuity level – Enginuity allows up to 128 Hyper Volumes to be configured from a single Physical Drive – Size of Volumes defined as number of Cylinders (FBA Cylinder = 15 * 32K), with a max. size ~32 GB – All Hyper Volumes on a physical disk do not have to be the same size however a consistent size makes planning and ongoing management easier EMC Global Education © 2004 EMC Corporation. All rights reserved. 32Volume specifications are illustrated here. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 33. Symmetrix Foundations, 33 Defining Symmetrix Logical Volumes Symmetrix Service Processor Physical Physical Physical Physical Physical Disk Disk Disk Disk Disk Running SymmWin Application Symmetrix Logical Volumes are configured using the service processor and SymmWin interface/application – EMC Configuration Group uses information gathered during pre-site survey to create initial configuration • Generate configuration file (IMPL.BIN) that is downloaded from the service processor to each director Most configuration changes can be performed on-line at the discretion of the EMC Customer Engineer Configuration changes can be performed online using the EMC ControlCenter Configuration Manager and Solutions Enabler Command Line Interface EMC Global Education © 2004 EMC Corporation. All rights reserved. 33The C4 group (Configuration and Change Control Committee) is the division of Global Services responsible for initialSymmetrix configuration and any subsequent changes to the configuration. They use time-honored and extensive bestpractices and tools to configure Symmetrix. There is also much manual review to be done to ensure that BIN files arevalid. An important misperception to correct is that only the CE can change the bin-file. While this might have beentrue at one time, today the customer may make configuration changes using EMC ControlCenter GUI or the SolutionsEnabler CLI.Prior to 5x66 Enginuity, BIN file configuration was performed using a DOS-based program called AnatMain. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 34. Symmetrix Foundations, 34 Symmetrix Logical Volume Types Open Systems hosts use Fixed Block Architecture (FBA) – Each block is a fixed size of 512 bytes – Sector = 8 Blocks (4,096 Bytes) Data Block – Track = 8 Sectors (32,768 Bytes) 512 Bytes – Cylinder = 15 Tracks (491,520 Bytes) – Volume size referred to by the number of Cylinders Mainframes use Count Key Data (CKD) – Variable block size specified in “count” Count Key Data – Emulate Standard IBM volumes • 3380D, E, K, K+, K++ (max. track size 47,476 bytes) • 3390-1, -2, -3, -9 (max. track size ~ 56,664 bytes) • Volume size defined as a number of Cylinders Symmetrix stores data in cache in FBA and CKD and on physical disk in FBA format (32 KB tracks) – Emulates “expected” disk geometry to host OS through Channel Directors EMC Global Education © 2004 EMC Corporation. All rights reserved. 34A notable exception to the “512-byte” Open Systems rule is AS/400. It uses 520 bytes per block. The extra 8 bytesare for host system overhead. Enginuity, prior to 5566 on the Symmetrix 5, only supports a single type of FBA formaton Open Systems drives. If you connect an AS/400 to a pre-5566 Symmetrix, all FBA devices must be formatted 520.Open Systems hosts other than the AS/400 must be configured to use 520-formatted volumes. BE AWARE THATCHANGING THE LOW-LEVEL FORMAT OF PHYSICAL DEVICES TYPICALLY REQUIRES SYMMETRIXDOWNTIME. Also, reformatting existing 512 devices will erase them, requiring a potentially complex backup andrestore of all Open Systems data. With 5566+ on Symm 5 +, Enginuity has SLLF (Selective Low-Level Format)capabilities. This allows some drives to be formatted 512 and others 520, avoiding the complications mentionedabove.The primary use for cache is for staging and destaging data between the host and the disk drives. Cache is allocated intracks and is referred to as cache slots, which are 32Kbytes in size (57 Kbytes for Mainframe). If the Symmetrix issupporting both FBA and CKD emulation within the same frame, the cache slots will be the size of the largest tracksize, 57K (3390) track size. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 35. Symmetrix Foundations, 35 Meta Volumes Between 2 and 255* Symmetrix Logical Volumes can be grouped into a Meta Volume configuration Logical and presented to Open System Volume 001 Meta hosts as a single disk Volume Logical LV 001 Allows volumes larger than the Volume 002 current maximum hyper volume LV 002 size of 32GB Logical – Satisfies requirements for Volume 003 LV 003 environments where there is a limited number of host addresses LV 00F Logical or volume labels available Volume 00F Data is striped or concatenated within the Meta Volume Stripe size is configurable *Note: Symmetrix Engineering – 2 Cylinders is the default size, recommends Meta Volumes no larger which is appropriate for most than 512GB environments EMC Global Education © 2004 EMC Corporation. All rights reserved. 35Meta Volumes allow customers to present larger Symmetrix Logical Volumes to the host environment. They are ableto present more GBs with fewer channel addresses. There is a limitation on the number of volumes a host can manage.For example, with NT, the Drive lettering puts a limit on the number of volumes, and Meta Volumes prevent “runningout of drive letters” by presenting larger volumes to NT hosts. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 36. Symmetrix Foundations, 36 Data Protection Data protection options are configured at the volume level and the same system can employ a variety of protection schemes – Mirroring (RAID 1) • Highest performance, availability and functionality • Two mirrors of one Symmetrix Logical Volume located on separate physical drives – Parity RAID • 3 +1 (3 data and 1 parity volume) or 7 +1 (7 data and 1 parity volume) • Formerly known as RAID S or RAID R – RAID 5 –Striped RAID Volumes • Data blocks are striped horizontally across the members of the RAID (4 or 8 volume) group • No separate parity drive, parity blocks rotate among the group members – RAID 10 – Mirrored Striped Mainframe Volumes – Dynamic Sparing • One or more HDAs that are used when Symmetrix detects a potentially failing (or failed) device • Can be utilized to augment data protection scheme • Minimizes exposure after a drive failure and before drive replacement – SRDF (Symmetrix Remote Data Facility) • Mirror of Symmetrix Logical Volume maintained in separate Symmetrix frame EMC Global Education © 2004 EMC Corporation. All rights reserved. 36RAID - Redundant Array of Independent DisksThe RAID Advisory Board has rated configurations with both SRDF and either Parity RAID or RAID 1 Mirroringwith the highest availability and protection classification: Disaster Tolerant Disk System Plus (DTDS+)See http://www.raid-advisory.com/emc.html for the ratings. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 37. Symmetrix Foundations, 37 Mirroring: RAID-1 Two physical “copies” or mirrors of the data Host is unaware of data protection being applied Different Disk Disk Director Director Physical Physical Logical Volume Drive 001 Drive LV 001 M2 Host Address Target = 1 LUN = 0 LV 001 M1 EMC Global Education © 2004 EMC Corporation. All rights reserved. 37Mirroring provides the highest level of performance and availability for all applications. Mirroring maintains aduplicate copy of a logical volume on two physical drives. The Symmetrix maintains these copies internally bywriting all modified data to both physical locations. The mirroring function is transparent to attached hosts, as the hostsview the mirrored pair of hypers as a single logical volume.Prior to the Symmetrix DMX, mirrors were configured with what is known as the “rule of 17”. Because of wherewithin the card cage the DA pairs reside (1/2, 3/4, 13/14, 15/16), as long as the sum of the DA director numbers equals17 (1/16, 2/15, 3/14, 4/13), the mirrors will always be on different internal system buses for the highest availability andmaximum Symmetrix resources. The Symmetrix DMX uses the rule of 17 for director failover pairing, and not volumemirroring. The point-to-point connections with cache eliminate the need for protection against a bus failure whilemirroring volumes. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 38. Symmetrix Foundations, 38 Mirror Positions Internally each Symmetrix Logical Volume is represented by four mirror positions – M1, M2, M3, M4 Mirror position are actually data structures that point to a physical location of a mirror of the data and status of each track Each mirror positions represents a mirror copy of the volume or is unused Symmetrix Logical Volume 001 M1 M2 M3 M4 EMC Global Education © 2004 EMC Corporation. All rights reserved. 38Before getting too far into volume configuration, understanding the concept of mirror positions is very important.Within the Symmetrix, each logical volume is represented by four mirror positions – M1, M2, M3, M4. These MirrorPositions are actually data structures that point to a physical location of a data mirror and the status of each track. Inthe case of SRDF, the mirror position actually points to a Logical Volume in the remote Symmetrix. Each positioneither represents a mirror or is unused. For example, an unprotected volume will only use the M1 position to point tothe only data copy. A RAID-1 protected volume will use the M1 and M2 positions. If this volume was also protectedwith SRDF, three mirror positions would be used, and if we add a BCV to this SRDF protected RAID-1 volume, allfour mirror positions would be used. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 39. Symmetrix Foundations, 39 Mirrored Service Policy Logical Volume Physical 000 Physical Drive Drive LV 000 M1 Logical Volume LV 000 M2 004 LV 004 M1 LV 004M2 Logical LV 008 M1 Volume 008 LV 008 M2 LV 00C M1 LV 00C M2 Logical Volume 00C Symmetrix leverages either or both mirrors of a Logical Volume to fulfill read requests as quickly and efficiently as possible Two options for mirror reads: Interleave and Split – Interleave maximizes throughput by using both Hyper Volumes for reads alternately – Split minimizes head movement by targeting reads for specific volumes to either M1 or M2 mirror Dynamic Mirror Service Policy (DMSP): policy is dynamically adjusted based on I/O patterns – Adjusted approximately every 5 minutes – Set at a logical volume level EMC Global Education © 2004 EMC Corporation. All rights reserved. 39During a read operation, if data is not available in cache memory, the Symmetrix reads the data from the volumechosen for best overall system performance. Performance algorithms within Enginuity track path-busy information, aswell as the actuator location, and which sector is currently under the disk head in each device. Symmetrix performancealgorithms for a read operation choose the best volume in the mirrored pair based on these service policies. • Interleave Service Policy – Share the read operations of a mirror pair by reading tracks from both logical volumes in an alternating method: a number of tracks from the primary volume (M1) and a number of tracks from the secondary volume (M2). The Interleave Service Policy is designed to achieve maximum throughput. • Split Service Policy – Different from the Interleave Service Policy because read operations are assigned to either the M1 or the M2 logical volumes, but not both. Split Service policy is designed to minimize head movement. • Dynamic Mirror Service Policy (DMSP) -DMSP dynamically chooses between the Interleave and Split policies at the logical volume level based on current performance and environmental variables, for maximum throughput and minimum head movement. DMSP adjusts each logical volume dynamically based on recent access patterns. This is the default mode. The Symmetrix system tracks I/O performance of logical volumes (including BCVs), physical disks, and disk directors. Based on these measurements, it directs read operation for mirrored data to the appropriate mirror. As the access patterns and workloads change, the DMSP algorithm analyzes the new workload and adjusts the service policy to optimize performance. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 40. Symmetrix Foundations, 40 Symmetrix RAID 10 (Mirrored Striped Mainframe Volumes with DMSP) EMC Global Education © 2004 EMC Corporation. All rights reserved. 40To improve mainframe volume performance, Symmetrix RAID 10 stripes data of logical devices across multipleSymmetrix logical devices.Four Symmetrix devices (each one-fourth the size of the original mainframe device) appear as one mainframe deviceto the host.Any four Symmetrix logical devices can be chosen to define a RAID 10 group provided they are the same type (forexample, IBM 3390) and have the same mirror configuration. Striping occurs across this group of four devices with astriping unit of one cylinder, as shown in the diagram. Since each member of the stripe group is mirrored, the entire setis protected. Dynamic Mirror Service Policy (DMSP) can then be applied to the mirrored devices. The combinationof DMSP with mirrored striping and concatenation to create a mainframe volume as illustrated, enables greatlyimproved performance in mainframe system Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 41. Symmetrix Foundations, 41 Symmetrix RAID-10 Meta volume Host I/O M1 M2 Vol A Vol A Vol A Vol A Cylinders Cylinders Cylinders Cylinders 1, 5, 9….. 2, 6, 10….. DMSP 1, 5, 9….. 2, 6, 10….. Vol A Vol A Vol A Vol A Cylinders Cylinders Cylinders Cylinders 3, 7, 11….. 4, 8, 12….. 3, 7, 11….. 4, 8, 12….. EMC Global Education © 2004 EMC Corporation. All rights reserved. 41This is a diagram of a RAID-10 stripe group. The portion of the logical volume which resides on one physical volumeis called a stripe. Each RAID-10 stripe group consist of four stripes distributed across four physical volumes. These aremirrored to consist of eight total physical volumes. The stripe group is constructed by alternately placing one cylinderacross each of the four physical volumes. These physical volumes cannot be on the same DA. The eight physicalvolumes are distributed across the Symmetrix back end for additional availability and improved performance. TheDMSP feature, which is available in all Symmetrix systems, allows the Enginuity algorithms to dynamically optimizehow the read requests can be satisfied over any of the eight physical devices. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 42. Symmetrix Foundations, 42 Symmetrix Parity RAID Vol A Vol B Vol C + Parity ABC 3 Host addressable volumes Not host addressable • 3 +1 (3 data volumes and 1 parity volume) or 7 +1. • Parity calculated by Symmetrix Disk Drives using Exclusive-OR (XOR) function. • Parity and difference data (result of XOR calculations) passed between drives by DAs. • Member drives must be on different DA ports (ideally on different DAs). • Parity volumes distributed across member drives in RAID Group. EMC Global Education © 2004 EMC Corporation. All rights reserved. 42Parity RAID is also referred to as RAID-S in Symmetrix 5 and earlier architectures. EMC’s Parity RAID DOES NOTSTRIPE DATA. Parity RAID employs the same technique for generating parity information as many othercommercially available RAID solutions, that is, the Boolean operation EXCLUSIVE OR (XOR). However, EMC’sParity RAID implementation reduces the overhead associated with parity computation by moving the operation fromcontroller microcode to the hardware on the XOR-capable disk drives.Symmetrix Parity RAID is not offered as a performance solution • For high data availability environments where cost and performance must be balanced • Fixed 3 + 1 configuration means 25% of disk space used for protection • Avoid in application environments that are 25% or greater write intensive • Every write to a data volume requires an update (write) to the parity volume within that rank or group • Write activity to the parity volume equals the total writes to the 3 data volumes within that rank or group • In write intensive environments, the parity volume is likely to reach its Fast Write Ceiling sending the entire rank into delayed write modeIf customer requirements dictate using Parity RAID, planning and careful attention to layout is required to ensureoptimal performance. In some configurations, Parity RAID in a DMX environment may perform as well as RAID 1protection on a Symmetrix 8000 Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 43. Symmetrix Foundations, 43 Symmetrix RAID-5 (4 members) Volume A 1 Host Addressable volume Parity 123 Data 1 Data 2 Data 3 Data 4 Parity 456 Data 5 Data 6 Data 7 Data 8 Parity 789 Data 9 Volume A with parity rotated among members EMC Global Education © 2004 EMC Corporation. All rights reserved. 43Raid-5 Groups can have 4 or 8 members per logical device • 4 members per logical device = 3 RAID-5 • 8 members per logical device = 7 RAID-5This example shows a single Logical volume in a Raid-5 Group (Stripe width is 4 tracks).Note that the data and parity tracks of a RAID-5 device are striped across 4 members.No separate parity drive or volume; parity blocks rotate among the group members Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 44. Symmetrix Foundations, 44 Dynamic Sparing Dynamic Spare Dedicated spare(s) disk protects storage Disk errors are detected during I/O operations or through DAs’ “Disk Scrubbing” Data from failed disk is copied to Dynamic Spare When failed disk is replaced, data is automatically restored and Dynamic Spare resumes role as standby EMC Global Education © 2004 EMC Corporation. All rights reserved. 44Every Symmetrix logical volume has 4 mirror positions. There is no priority associated with any of these positions.They simply point to potential physical locations on the back end of the Symmetrix for the logical volume entity.When sparing is necessitated, hyper volumes on the spare disk devices take the next available mirror position for thelogical volumes present on the failing volume. All of these dynamic spare hyper volumes are marked as having alltracks invalid in the respective mirror positions of the logical volumes. It is now the responsibility of the Symmetrix tocopy all tracks over to the Dynamic Spare.Dynamic sparing occurs at the physical drive level, since a physical drive is the FRU (Field Replaceable Unit) in theSymmetrix. In other words, you can’t just replace a failed hyper volume, only the disk it resides on. However, theactual data migration from the volumes on the failed drive to the dynamic spare occurs at the logical volume level.Dynamic Sparing is also supported with Parity RAID, a minimum of 3 spares is suggested. If a drive fails, a dynamicspare drive will copy the data volumes onto itself by rebuilding them from parity and reading from any remaininguncorrupted data. If there are at least 3 spares available, the 1st spare will also start copying data from uncorrupteddrives in the group. The other 2 spares will copy the contents of the remaining data volumes on the unaffected drivesin the group. This results in the formerly parity-protected volumes now being temporarily mirrored. Since parity can’tbe calculated with a drive lost, and mirroring is a faster way to make sure the data is redundantly protected, mirroringthe entire RAID group results in the best way to protect against data loss until the problematic drive can be replaced. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 45. Symmetrix Foundations, 45 SRDF Introduction Symmetrix Remote Data Facility (SRDF) maintains real-time or near real-time copy of data at remote location Similar concept as RAID-1 except mirror is located in a different Symmetrix Primary copy is called Source, remote copy is called Target Link options between local and remote Symmetrix based on distance and performance requirements – ESCON – Fibre Channel – Gigabit Ethernet Source Target EMC Global Education © 2004 EMC Corporation. All rights reserved. 45SRDF is an online, host-independent, mirrored data storage solution that duplicates production site data (source) to asecondary site (target). If the production site becomes inoperable, SRDF enables rapid manual fail over to thesecondary site, allowing critical data to be available to the business operation in minutes. While it is easy to see this asa disaster recovery solution, the remote copy can also be used for business continuance during planned outages as wellas backups, testing, and decision support applications. EMC offers a complete set of replication solutions to meet awide range of service level requirements. When implementing a remote replication solution, users must balanceapplication response time, recovery point objectives, and communications and infrastructure costs. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 46. Symmetrix Foundations, 46 TimeFinder Introduction TimeFinder allows local replication of Symmetrix Logical Volumes for business continuance operations Utilizes special Symmetrix Logical volume called a BCV STD BCV or Business Continuance Volume BCV STD BCV – BCV can be dynamically Established attached to another volume, synchronized, and split off BCV Split – Host can access BCV as an 1. “Establish” BCV independent volume that may 2. Synchronized be used for business 3. “Split” BCV continuance operations 4. Execute BC operations – Full volume copy using BCV EMC Global Education © 2004 EMC Corporation. All rights reserved. 46TimeFinder uses Business Continuance Volumes (BCVs) to create copies of a volume for parallel processing.Basic TimeFinder operations include: • Establish Mirror relationship between any standard volume and BCV. Basically, the BCV assumes the next available mirror position of the source volume. While a BCV is established, it is “hidden” from view and cannot be accessed. • Synchronize data from Source to BCV. Synchronization will take place while production continues on the source volume. TimeFinder supports incremental establish by default where only changed data since the last establish is synchronized. • Split allows the BCV to be accessed as an independent volume for parallel processing. • Restore allows the BCV to be established as a mirror to either the original source or a different volume and the data on the BCV is synchronized. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 47. Symmetrix Foundations, 47 EMC SNAP Introduction Production view EMC SNAP uses Snapshot techniques of volume to create logical point-in-time images of a source volume Volume A – Snapshot is a virtual abstraction of a volume – Multiple Snapshots can be created from same source Snapshot Snapshot view – Snapshots are available immediately of of volume Volume A EMC SNAP does a Copy-on-Write (VDEV) – Writes to production volume are first copied to Save Area – Uses only a fraction of the source Save Area volume’s capacity (~20–30%) Original data copied to Save Area prior to Snapshots can be used for both read new production writes and write processing – Reads of unchanged data will be from Production volume – Changed data will be read from Save Area EMC Global Education © 2004 EMC Corporation. All rights reserved. 47EMC Snap creates space-saving, logical point-in-time images or “snapshots.” The snapshots are not full copies of data;they are logical images of the original information based on the time the snapshot was created. It’s simply a view intothe data. A set of pointers to the source volume data tracks is created instantly upon activation of the snapshot. Thisset of pointers is addressed as a logical volume and is made accessible to a secondary host that uses the point-in-timeimage of the data. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 48. Symmetrix Foundations, 48 Symmetrix Availability: Phone-Home and Dial-In EMC Phone-Home capability – Service Processor connects to external modem – Communicates error and diagnostic information to EMC Customer Service Dial-In capability – Provides problem resolution – Product Support Engineer (PSE) or Customer Engineer (CE) dial-in – Allows full control of service processor through proprietary and secure interface – Allows for proactive and reactive maintenance – Can be disabled by customer through external modem EMC Global Education © 2004 EMC Corporation. All rights reserved. 48Every Symmetrix unit has an integrated service processor that continuously monitors the Symmetrix environment. Theservice processor communicates with the EMC Customer Support Center through a customer-supplied, direct phoneline. The service processor automatically dials the Customer Support Center whenever Symmetrix detects a componentfailure or environmental violation. An EMC Product Support Engineer at the Customer Support Center can also rundiagnostics remotely through the service processor to determine the source of a problem and potentially resolve itbefore the problem becomes critical. When required, a Customer Engineers will be dispatched to the Symmetrix toreplace hardware or perform other maintenance. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 49. Symmetrix Foundations, 49 Course Summary The key points covered in this course include: Redundancy in the hardware design, and intelligence through Enginuity, allow Symmetrix to provide the highest levels of data availability Symmetrix basic architecture is comprised of three functional areas (Front End, Back End and Shared Global Memory) connected by internal system buses All I/O must be serviced through cache (read hit, read miss, fast write, delayed write) Symmetrix physical disk drives are divided into Hyper Volumes, which form Symmetrix Logical Volumes, that are presented to the host environment as if they were entire physical drives Mirroring, Parity RAID, SRDF, and Dynamic Sparing are all media protection options available on Symmetrix EMC Global Education © 2004 EMC Corporation. All rights reserved. 49These are some of the main features of the Symmetrix. Please take a moment to read them. Copyright © 2004 EMC Corporation. All Rights Reserved.
  • 50. Symmetrix Foundations, 50 Closing Slide EMC Global Education © 2004 EMC Corporation. All rights reserved. 50Thank you for your attention. This ends our training on Symmetrix Foundations. Copyright © 2004 EMC Corporation. All Rights Reserved.