IT Handbook - Storage: The Backbone of your Virtual Environment


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Virtualization has made shared storage a new reality in data centres. Learn which technologies offer the best fit and how to pinpoint the source of possible problems.

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IT Handbook - Storage: The Backbone of your Virtual Environment

  2. 2. EVALUATING STORAGE FOR VIRTUAL ENVIRONMENTS Evaluating Storage for Virtual Environments with server virtualization, operating systems and applications are noEVALUATING STORAGE FOR longer tied to one specific piece of hardware. They can move from machine toVIRTUAL ENVIRONMENTS machine—either manually or automatically—and their data must be able to follow. Shared storage makes that happen.TESTING STORAGE So what exactly is shared storage? It refers to a device or devices that storeFOR VIRTUALIZATION data for and are accessible by multiple systems over a network. In addition to providing the flexibility needed to support virtualization, shared storage alsoEXPLORING ADVANCEDSTORAGE FEATURES increases efficiency. When servers don’t have to spend the resources to store data locally or transmit data to attached devices, they can use that processingTROUBLESHOOTING power to handle more workloads—or more intensive workloads—which helpsSTORAGE server consolidation. There are two main storage approaches for virtualization: storage area net- works (SANs), which typically use iSCSI or Fibre Channel technologies, and network-attached storage (NAS). Each technology has its pros and cons. Your organization’s goals, size and budget—among other factors—will determine which technology or blend of technologies is a good fit for your virtualization project. FIBRE CHANNEL SAN A SAN uses block-level storage, which relies on a filing system to write and re- trieve data. It provides high performance, but it can be expensive and complex. Cost and complexity can be prohibitive for small and medium-sized busi- nesses for whom the costs of buying, installing and managing a SAN may out- weigh the savings that would result from consolidating a few physical servers. Despite these issues, SAN technology is still a popular choice for virtualization storage, especially among larger organizations. That’s because many SANs rely on Fibre Channel networking, which provides high-speed data transmission. 2 S T O R A G E : T H E B A C K B O N E O F Y O U R V I R T UA L E N V I R O N M E N T
  3. 3. EVALUATING STORAGE FOR VIRTUAL ENVIRONMENTS The speed of data transmission is essential in virtual environments, espe- cially when it comes to performance. After all, it doesn’t matter how fast a phys- ical server and its virtual machines (VMs) can process data if the data is slow in arriving to those systems in the first place. For some workloads, such as test and development projects, a certain amount of lag time may be acceptable. But for oth-EVALUATING STORAGE FORVIRTUAL ENVIRONMENTS ers, such as databases or Web servers, max- The speed of data imum performance is a must. transmission isTESTING STORAGE When calculating potential return on in- essential in virtualFOR VIRTUALIZATION vestment (ROI) in a Fibre Channel SAN, or- environments, espe- ganizations should consider speed because cially when it comesEXPLORING ADVANCED it will affect backup and recovery. SomeSTORAGE FEATURES businesses start losing money the second a to performance. certain application goes down, and theTROUBLESHOOTINGSTORAGE bleeding doesn’t stop until the application comes back up. In these cases, speed is of the utmost importance, and the ROI of Fibre Channel is clear. But for or- ganizations that can tolerate some downtime, Fibre Channel might not be worth the money. FIBRE CHANNEL OVER ETHERNET For organizations looking to realize the benefits of Fibre Channel with less cost and complexity, Fibre Channel over Ethernet (FCoE) is an emerging alternative. The FCoE protocol lets organizations use their existing Ethernet infrastruc- tures to transmit data across a SAN. Because of that, it requires fewer cables and network cards, which can reduce the cost of a SAN implementation. Despite these benefits, FCoE does have some drawbacks. The speed of exist- ing Ethernet networks has raised concerns among some administrators. But as more organizations move from 1-Gigabit Ethernet to 10-Gigabit Ethernet, that becomes less of an issue. Other businesses are hesitant to add storage traffic to their existing Ethernet 3 S T O R A G E : T H E B A C K B O N E O F Y O U R V I R T UA L E N V I R O N M E N T
  4. 4. EVALUATING STORAGE FOR VIRTUAL ENVIRONMENTS networks because of the added management it requires—and the friction it can cause between storage administrators and network administrators. iSCSI SAN Another SAN option is iSCSI, a protocol that arrived after many organizationsEVALUATING STORAGE FORVIRTUAL ENVIRONMENTS had already adopted Fibre Channel. Like FCoE, iSCSI can run over Ethernet networks, and that can result in cost savings and reduced management com-TESTING STORAGE plexity.FOR VIRTUALIZATION Organizations that choose iSCSI can use their existing networks without having to buy the expensive switches, adapters and other equipment requiredEXPLORING ADVANCED to support Fibre Channel. Plus, administrators don’t have to learn how to man-STORAGE FEATURES age a whole new network. Some experts say that performance takes a hit on an iSCSI SAN compared toTROUBLESHOOTINGSTORAGE Fibre Channel. Others say that a properly configured iSCSI SAN can reach sim- ilar performance levels. NETWORK-ATTACHED STORAGE The SAN versus NAS debate is similar to the Fibre Channel versus iSCSI de- bate in that each centers on both cost and performance. Unlike a SAN, NAS takes a file-level approach to storage for virtualization. The additional layer of abstraction that a SAN provides isn’t there with NAS, so there’s less complexity and, therefore, lower costs. But security is an added concern when using NAS for virtualization storage. Because NAS stores the file systems, anyone who can access the NAS device can access those files if they have the proper privileges. SANs control security themselves, regardless of the security levels of individual file systems. Having options can help organizations come up with the best solutions. In the next segment, learn how to test each approach and determine which is best for your environment. I 4 S T O R A G E : T H E B A C K B O N E O F Y O U R V I R T UA L E N V I R O N M E N T
  5. 5. TESTING STORAGE FOR VIRTUALIZATION Testing Storage for Virtualization you can do all the research in the world, but the only way to make sure you have the right storage for your virtual environment is to test it. It’s important to test your storage to find out which results require the most attention.EVALUATING STORAGE FORVIRTUAL ENVIRONMENTS As of now, the use of solid-state drives (SSD) is not commonplace. Even if it were, all the available shared storage technologies communicate over a wireTESTING STORAGE from the virtualization host to a storage array. This wire either communicatesFOR VIRTUALIZATION using Fibre Channel protocol, iSCSI, a network file system or Fibre Channel over Ethernet.EXPLORING ADVANCED These protocols and the speeds at which the data is transmitted across theSTORAGE FEATURES wire are often seen as limiting factors in storage. Also consider all the devices on the path to the disk where the data will eventually be saved. This includesTROUBLESHOOTINGSTORAGE such things as host bus adapters, local cache, Ethernet or Fibre Channel switches, storage processors, disk controllers and the spindles on each of the disks, if you are not using SSD. STORAGE AS A SHARED RESOURCE In addition to the hardware considerations, remember that storage in a virtual environment is a shared resource—shared not only among VMs running on a host but also among hosts. So any technology used for storage—whether file sharing or block storage—must support clustered file systems. That implies some ability to minimally lock the file system table of contents to ensure up- dates are serialized across all hosts. This type of locking often adds quite a bit of complexity into a seemingly sim- ple storage system. Now add the ability to have multiple storage paths from the VM to the storage device, and you will see that real-world testing is often re- quired in the form of a bake-off between storage vendors. The tests are intended to determine two things: one is performance of reads 5 S T O R A G E : T H E B A C K B O N E O F Y O U R V I R T UA L E N V I R O N M E N T
  6. 6. TESTING STORAGE FOR VIRTUALIZATION and writes through the virtual environment—often referred to as latency—and the other is the maximum number of I/O operations per second (IOPS) that can take place to and from the storage device without increasing latency. IOPS can also be seen as a measure of the number of VMs a particular storage device can handle per logical unit, or LUN, of the storage device. In some cases, using more LUNs will decrease lock operations. It will also in-EVALUATING STORAGE FORVIRTUAL ENVIRONMENTS crease IOPS when a LUN is locked because no operations can take place for the length of the lock, which is usually less than 10 microseconds. But becauseTESTING STORAGE quite a few writes or reads can takeFOR VIRTUALIZATION place during 10 microseconds, it’s im- portant to remember that IOPS and la- If your QA environmentEXPLORING ADVANCEDSTORAGE FEATURES tency values will suffer if the lock matches your production extends past the desired time. environment, you haveTROUBLESHOOTING a ready-built test envi-STORAGE CREATING A REAL-WORLD ronment. If your QA TEST ENVIRONMENT environment does not When setting up a test for your storage match your production subsystem, create as close to a real- environment, then you world test as possible. Ideally, you have your work cut out would put the new storage system into for you. your QA lab and then move via Stor- age vMotion or otherwise migrate your real test environment to the new storage device. If your QA environment matches your production environment, you have a ready-built test environment. If your QA environment does not match your production environment, then you have your work cut out for you. For better results, you may consider trying to match your QA environment as closely as possible to your production environment in your count of application instances, quantity of transactions and data per transaction. If your QA envi- ronment does not match your production environment, your storage latency 6 S T O R A G E : T H E B A C K B O N E O F Y O U R V I R T UA L E N V I R O N M E N T
  7. 7. TESTING STORAGE FOR VIRTUALIZATION and IOPS values as well as counts of VMs per LUN will not be accurate and may actually be quite a bit worse than expected when you finally place the cho- sen storage device into production. TWO TESTS TO CONSIDEREVALUATING STORAGE FORVIRTUAL ENVIRONMENTS There are at least two tests to consider: those that have many small virtual disks per LUN and those that have a few large virtual disks per LUN. If you are test-TESTING STORAGE ing Tier 1 applications, you may also have raw disk maps for very large LUNs toFOR VIRTUALIZATION hold data such as a database or an extremely large file share. Ensure that your test mimics the realEXPLORING ADVANCED world as much as possible. DetermineSTORAGE FEATURES your max throughput by inputting trans- Once you have actions in your environment as fast as completed your testing,TROUBLESHOOTINGSTORAGE you possibly can. Next, use a real-world you can then choose quantity of transactions to determine the proper layout of your steady-state numbers. your storage within It is important to use the proper tools the virtual environ- to determine latency and IOPS values. ment and the proper Such tools will be able to get performance data directly from the array as well as de- storage subsystem. termine how your virtual environment sees the performance—both are required. Once you have completed your test- ing, you can then choose the proper layout of your storage within the virtual en- vironment and the proper storage subsystem. The key for this type of testing is good planning, suitable documentation and a good test suite that is as real- world as possible. I 7 S T O R A G E : T H E B A C K B O N E O F Y O U R V I R T UA L E N V I R O N M E N T
  8. 8. EXPLORING ADVANCED STORAGE FEATURES Exploring Advanced Storage Features storage can enhance your virtual environment. Adding advanced features such as data deduplication, thin provisioning and others can actually improve virtualization performance and reduce your storage footprint.EVALUATING STORAGE FORVIRTUAL ENVIRONMENTS Storage is one of the more expensive parts of any virtual environment. Be- cause of that, use this limited resource sparingly. The good news is that today’sTESTING STORAGE technology helps administrators use storage more efficiently.FOR VIRTUALIZATION Some technologies that aid efficiency are in hardware, such as data dedupli- cation. Others are not, such as thin provi-EXPLORING ADVANCED sioning and linked clones. All theseSTORAGE FEATURES Data deduplication technologies are designed to allow ad- mins to use limited storage capabilities allows a storage deviceTROUBLESHOOTINGSTORAGE better. to condense identical blocks of data down to one block with a link HOW DATA DEDUPLICATION WORKS back to that block per Data deduplication allows a storage de- LUN and sometimes vice to condense identical blocks of data down to one block with a link back to across LUNs. that block per LUN and sometimes across LUNs. This happens within the storage processor and is possible only because of advancements in processor capabilities such as multiple cores. In some cases, data deduplication happens after the fact as a background task. Until the deduplication task is completed, the number of actual blocks of disk being used may change. Deduplication is extremely useful for unencrypted data because once the data is encrypted, deduplication would be minimal. While already removing like blocks from a file, compressed data may still participate in deduplication because many compressed files of similar construct can still be deduplicated. 8 S T O R A G E : T H E B A C K B O N E O F Y O U R V I R T UA L E N V I R O N M E N T
  9. 9. EXPLORING ADVANCED STORAGE FEATURES Encryption attempts to avoid having the data appear the same twice, regardless of similarities. On the other hand, thin provisioning is a technology that allocates only the in-use blocks of a file or virtual disk instead of the completely requested alloca- tion of blocks. Thin provisioning could work with data deduplication to use even fewer blocks of disk than previous thought because instead of allocatingEVALUATING STORAGE FORVIRTUAL ENVIRONMENTS blocks to participate in deduplication, the blocks are not allocated until needed. Unfortunately, there is no way to prevent a thin provisioned file or vir-TESTING STORAGEFOR VIRTUALIZATION tual disk from allocating all its blocks. Linked clones tied to Because of that, either could easily use thin provisioning andEXPLORING ADVANCED much more storage than originally en- data deduplicationSTORAGE FEATURES visioned. could lead to quite a fewTROUBLESHOOTING storage blocks saved onSTORAGE a storage device. ADVANTAGES OF LINKED CLONES Linked clones provide the ability to link one virtual disk to another virtual disk in such a way that only the changes between the original virtual disk and the cloned virtual disk are recorded within the clone. This is an extremely useful construct if a base part of a virtual disk does not change, such as in the operating system of a VM. The linked clone would instead contain only those changes required for a given application, user or service. Linked clones tied to thin provisioning and data deduplication could lead to quite a few storage blocks saved on a storage device. But a linked clone can grow to the full size of the original disk if the blocks of the original disk are changed in any way, such as the case of an operating sys- tem patch or disk optimization performed from within the linked clone. Linked clones have a further limitation in the depth of clones. The more depth to the clones, the slower the virtual disk will be because of the block fix- ups that are required. 9 S T O R A G E : T H E B A C K B O N E O F Y O U R V I R T UA L E N V I R O N M E N T
  10. 10. EXPLORING ADVANCED STORAGE FEATURES WEIGHING STRENGTHS AND WEAKNESSES If used correctly, all of these technologies could reduce the overall quantity of storage required for your virtual environment, but each has its own weak- nesses and strengths. One weakness is that to use vSphere Fault Tolerance, the virtual disk must not be thin provisioned or a link cloned. What is required is a thickly allocated disk, meaning that all blocks are allocated and in use.EVALUATING STORAGE FORVIRTUAL ENVIRONMENTS Data deduplication will not produce the same results if data is encrypted before being written to the storage array. That is the only way it would hap-TESTING STORAGE Data deduplicationFOR VIRTUALIZATION pen with today’s technology. Always use care with tools such as will not produce theEXPLORING ADVANCED thin provisioning and linked clones be- same results if data isSTORAGE FEATURES cause these technologies can easily be encrypted before being abused. Any savings you thought you written to the storageTROUBLESHOOTINGSTORAGE would receive would be incorrect be- array. That is the only cause of sudden growths of the virtual way it would happen disks to full sizes. The truly inconsiderate component of with today’s technology. these sudden growths is that technology does not yet exist to tell you that this is eminent. The virtual environments re- port the full size of the virtual disks instead of the allocated sizes, and the stor- age devices report only on what space is left, not on what space is available on a per-file basis. So use extreme care and audit results when using these technologies. Some form of continual monitoring may be required if space on your storage arrays suddenly grows. Thin provisioning and linked clones are ways to fit more virtual disks per LUN and to make better use of your storage device. Alternately, data deduplica- tion has no such limits unless the data is encrypted. The bottom line is to use caution when choosing these technologies, and know their limitations. I 10 S T O R A G E : T H E B A C K B O N E O F Y O U R V I R T UA L E N V I R O N M E N T
  11. 11. TROUBLESHOOTING STORAGE Troubleshooting Storage problems are bound to pop up no matter how well you have researched and implemented storage in your virtual environment. Uptime and I/O speed can be challenging to maintain. The best defense is to find out how to locate theEVALUATING STORAGE FORVIRTUAL ENVIRONMENTS source of possible problems and fix them. In general, once you have a properly configured storage subsystem that isTESTING STORAGE built to meet the requirements of your virtual environment, there is often noFOR VIRTUALIZATION need to modify the environment unless something changes. Those changes can include adding more applications to the original mix or adding new applicationEXPLORING ADVANCEDSTORAGE FEATURES functionalities that require more storage. Some changes could be more subtle. Connection issues happen occasionally,TROUBLESHOOTING and usually the first to fail is the virtualization host. Modern virtualizationSTORAGE hosts are good at connecting to storage that has been properly presented and zoned to the virtual environment. If there is a connectivity issue, it is essential to first check the hardware in- volved for proper connections—such as making sure lights are properly lit— and then check the zoning and presentation of the LUN to the virtualization host. It should be noted that some hypervisors limit the number of LUNs that can be used. LOCKING STORAGE SUBSYSTEMS Locking is required when dealing with files that are shared and that cross host boundaries. So, at a minimum, the table of contents of each file system should be locked. When virtualization first started, locking storage subsystems was a prevalent problem. But with modern hypervisors, many of these issues have been solved by applying even more technology such as segmented table of contents, in- creased lock time-outs and increased number of lock retries. 11 S T O R A G E : T H E B A C K B O N E O F Y O U R V I R T UA L E N V I R O N M E N T
  12. 12. TROUBLESHOOTING STORAGE Storage subsystems have also improved, but problems still arise occasionally. A more prevalent issue is SCSI reservation time-out, which means the lock failed so the data was only partly written or not written at all. No one wants to see a time-out error message in a vSphere log file because it implies something went seriously wrong. Before reviewing all disk write ac- tions that have taken place, don’t forget to inspect the hardware.EVALUATING STORAGE FORVIRTUAL ENVIRONMENTS Because most people assume the hardware is not at fault, a hardware inspec- tion is often performed last. But, for locking issues, the reverse is often true.TESTING STORAGE After inspecting the hardware, review other types of actions that may causeFOR VIRTUALIZATION locks. Investigate anything that changes the table of contents of the clustered file system.EXPLORING ADVANCED Performance issues are those stemming from the measured or perceivedSTORAGE FEATURES slowness of an application. The first thing to understand about performance is that it may not be the storage subsystem, but you’ll need the proper tools to de-TROUBLESHOOTINGSTORAGE termine if this is actually true. WHICH TOOLS TO USE Modern virtual environments have several built-in management tools that will show the LUN latency values as well as the number of IOPS in use. Many third- party tools also give the same data. Getting this data as close to the hardware is often paramount to determining what is actually going on. One helpful tool is NetApp Balance, which correlates VM activity with the activity on the LUN of the questionable storage array. If latency is high, then re- balance the data across LUNs and perhaps across storage paths until there is a better latency score. Changing storage paths could also imply moving the load from one virtual- ization host to another. For these tasks, vSphere Storage vMotion and vMotion or Xen/Hyper-V Live Migration tools can be extremely useful. There is no easy fix for a large number of IOPS unless you have control over the application and can spread the load across multiple LUNs with data- 12 S T O R A G E : T H E B A C K B O N E O F Y O U R V I R T UA L E N V I R O N M E N T
  13. 13. TROUBLESHOOTING STORAGE splitting or caching technologies or can use massively parallel databases such as Greenplum. But even with technologies like these, the solution is often to re- vamp an application instead of bolting on a solution. And vSphere’s Storage IO Control (SIOC) functionality could also be used to give higher priority to writes made by those applications marked as critical or those that have an increased amount of shares of the storage path than otherEVALUATING STORAGE FORVIRTUAL ENVIRONMENTS virtual disks on the same path. But SIOC is a contention-based tech- nology based on LUN latency values. If Multipath-pluginTESTING STORAGEFOR VIRTUALIZATION the latency values are below 30 mi- tools allow you to use croseconds, then SIOC is not in use. tools provided by theEXPLORING ADVANCEDSTORAGE FEATURES Multipath-plugin tools are also help- storage vendors to ful. They allow you to use tools provided aggregate, load balance by the storage vendors to aggregate, loadTROUBLESHOOTING and better control howSTORAGE balance and better control how data is written to the storage array. data is written to the There is also an increase in using lo- storage array. calized SSD drives and storage cache cards to improve overall write and read times to and from the storage array. Writes hit the local cache and then are forwarded over the wire. Local reads of the same data are then accelerated, as is the response time for writes. Other issues can cause a malfunction in storage environments, such as a sud- den loss of connectivity or storage processor failures. These failures often show up as virtual environment issues and may be investigated within the virtual en- vironment first. Any failure will adversely affect your virtual environment. Storage failures can show up as other issues that suddenly increase latency and affect perform- ance It’s always a good idea to investigate the storage subsystem at the same time. I 13 S T O R A G E : T H E B A C K B O N E O F Y O U R V I R T UA L E N V I R O N M E N T
  14. 14. ABOUT THE AUTHORS Edward L. Haletky is the author of VMware vSphere and Virtual Infrastructure Security: Securing the Virtual Environment and VM- ware ESX and ESXi in the Enter- prise: Planning Deployment ofEVALUATING STORAGE FOR Virtualization Servers, 2nd Edi-VIRTUAL ENVIRONMENTS tion. He owns AstroArch Consulting EXECUTIVE EDITOR Jo Maitland Inc., which provides virtualization,TESTING STORAGEFOR VIRTUALIZATION security, network consulting and de- SITE EDITOR velopment, and The Virtualization Colin Steele Practice, where he is an analyst.EXPLORING ADVANCED SENIOR MANAGING EDITORSSTORAGE FEATURES Haletky is the moderator and host of Michelle Boisvert the Virtualization Security Podcast Lauren HorwitzTROUBLESHOOTING and moderator for the VMware Com-STORAGE MANAGING EDITOR munities Forums. Christine Casatelli ASSOCIATE MANAGING EDITORS Colin Steele is senior site editor Jeannette Beltran for Eugene Demaitre Martha Moore and, which pub- lish expert content for IT profession- DIRECTOR OF ONLINE DESIGN Linda Koury als working with server virtualiza- tion technology. Before joining EDITORIAL DIRECTOR TechTarget in 2007, he was a news- Cathleen Gagne paper reporter for The Eagle- PUBLISHER Tribune in North Andover, Mass. Marc Laplante Steele has previously written for the Gloucester Daily Times, Tri-Town TechTarget Transcript and The Daily Orange 275 Grove Street, Newton, MA 02466 at Syracuse University, where he received his bachelor’s degree in ©2011 TECHTARGET. ALL RIGHTS RESERVED. newspaper journalism in 2002. 14 S T O R A G E : T H E B A C K B O N E O F Y O U R V I R T UA L E N V I R O N M E N T
  15. 15. RESOURCES FROM OUR SPONSOR• How vStorage Enabled SANs Will Help Maximize VMware Investment• Virtualizing Microsoft Applications with VMware vSphere on Dell Servers and Dell EqualLogic Storage• Calculating Storage Requirements: Impact of Solid State Drives, Virtualization, and Cloud Computing