Storage Area Networks
Storage Area Networks - Defined
The Storage Networking Industry Association defines Storage Area
Networks as follows:
1. A network whose primary purpose is the transfer of data between
computer systems and storage elements and among storage
elements. Abbreviated SAN. A SAN consists of a communication
infrastructure, which provides physical connections, and a
management layer, which organizes the connections, storage
elements, and computer systems so that data transfer is secure and
robust. The term SAN is usually (but not necessarily) identified with
block I/O services rather than file access services.
2. A storage system consisting of storage elements, storage devices,
computer systems, and/or appliances, plus all control software,
communicating over a network.
SANs originated in the 1980s as a mainframe solution to storing large
amounts of data that was scalable and flexible with highly availability.
Storage area networks (SANs) are high performance networks dedicated
to delivering data between servers and storage.
Storage Area Networks - Architecture
A SAN consists of a communication infrastructure, which provides physical
connections, and a management layer, which organizes the connections,
storage elements, and computer systems so that data transfer is secure
Centralized and interconnected storage devices reside in the bottom tier of
the traditional 3-tiered client/server architecture.
Fibre Channel is the most widely used SAN technology because of its
speed, scalability and flexibility.
A SAN is typically based on one of two topologies:
– Arbitrated Loop is a classic ring topology that manages traffic flow. It
is a fairly inexpensive configuration for small and medium sized SANs.
– Switched Fabric provides full duplex communication between all
devices in the SAN. Fabric switches are considerably more expensive
than an arbitrated loop hub, but can provide each device on the SAN
an independent connection to every other device.
Storage Area Networks – Benefits
Using a SAN can potentially offer the following benefits:
– Improvements to application availability: Storage is independent of
applications and accessible through multiple data paths for better
reliability, availability, and serviceability.
– Higher application performance: Storage processing is off-loaded from
servers and moved onto a separate network.
– Centralized and consolidated storage: Simpler management,
scalability, flexibility, and availability.
– Data transfer and vaulting to remote sites: Remote copy of data
enabled for disaster protection and against malicious attacks.
– Simplified centralized management: Single image of storage media
Storage Area Networks - Considerations
• Data format
• Data can be stored as files, or in block format.
• SAN management architecture
• SAN storage level
• SAN network level
• Enterprise systems level
• Security in a LAN environment can be complex.
• When utilizing multiple storage servers, it is critical that one server
cannot overwrite another's information.
• Access control is also extremely important.
Storage Area Networks – Management
SAN Storage Level
– Consists of storage devices such as disks, disk arrays, tapes and tape
– The ANSI SCSI-3 serial protocol is used by many SAN vendors in order
to offer higher speeds, longer distances, and greater device population
for SANs, with few changes in the upper level protocols. This protocol
defines a new set of commands called SCSI Enclosure Services (SES)
for basic device status from storage enclosures.
Storage Area Networks – Management
SAN Network level
– Consists of SAN cables, SAN hubs, SAN switches, inter switch links,
SAN gateways, and Host bus adapters (HBAs).
– Closely tied to local area network (LAN) and wide area network (WAN)
infrastructures. The hubs, switches, gateways, and cabling use Simple
Network Management Protocol (SNMP) to manage all of these
networking components. Most SAN solution vendors require SNMP
support to be used by SNMP based network management applications.
Storage Area Networks – Management
SAN Enterprise level
– The enterprise systems level essentially ensures the ability to have a
single management view and console.
– Enterprise systems management applications gather and present all
management data in a single web-based management tool. Data
comes storage devices, networks, servers, and desktops.
– Common interfaces include:
Web-Based Enterprise Management
Common Information Model
Application Program Interface
Java Management API
Desktop Management Interface
Storage Area Networks – Security
A storage device is connected to many systems, and must protect:
– Confidentiality of data
– Integrity of data
– Against unauthorized deletion of data
– Loss of access to data
Storage Area Networks - Security
Recommended steps to minimize the risks :
Administrative tasks require administrator log in access.
Devices must log in to the storage network before gaining access
to the data.
Individual administrators have permissions to only perform specific
actions on specific devices.
Storage devices validate rights to data to prevent access from an
All administrative changes and significant events are logged to
track changes and trace problems.
– Encryption (not yet in widespread use)
Protects both confidentiality and integrity of data.
Storage Area Networks – Network Technologies
Fibre Channel over IP
Fibre Channel over ATM
Fibre Channel over SONET
Fibre Channel over dark fiber or DWDM
Storage Area Networks – Fibre Channel
Fibre Channel is the predominate SAN technology since it:
– Provides a high-speed, non-blocking architecture
– Scales from 133 Mbps to 1 Gbps and beyond
– Allows different high-level protocols (IP, ATM, etc.) to operate over its
– Can connect nodes up to 10 kilometers (over 6 miles) apart.
Fibre Channel can attach devices through a number of methods like loops,
hubs, and switches.
– Hubs make loop simulate a series of point-to-point connections.
– Switches permit multiple devices to be connected via multiple loops,
thereby multiplying bandwidth. Multiple 100-MBps loop configurations
can be managed through one central point.
– Fabrics, composed of multiple switches, enable Fibre Channel
networks to grow to very large sizes, that offer extremely high
bandwidth. Fabrics can span very large geographic areas.
These features make fibre channel a fast, stable, and flexible technology
for storage area networks.
Storage Area Networks – FCIP
Fibre Channel over IP combines proven technologies to accomplish the
transfer of storage data within SAN. Fibre Channel provides software
compatibility, interoperability, and proven applications for storage
networking. IP facilitates the movement of data across WANs and is a
proven application for WAN-based data networking.
Fibre Channel over IP solutions enables Fibre Channel frames to be
encapsulated in TCP packets that are transported over the IP network.
Overall performance is dependent on the types of switches and routers,
the number of hops and the amount of congestion in the network.
Fibre Channel over IP is currently a very cost-effective technology for
asynchronous applications such as remote data backup.
The IETF standards organization is currently developing specifications to
allow the transport of Fibre Channel data over IP networks.
Storage Area Networks – iSCSI
iSCSI is an emerging standard which defines the encapsulation of SCSI
packets in TCP. These packets are then routed using IP. This technology
allows block-level storage data to be transported over widely used IP
networks, enabling end users to access the storage network from
anywhere in the enterprise.
Several iSCSI products are now available, including iSCSI HBAs and iSCSI-
to-Fibre Channel storage routers. Storage routers, when utilized with a
Fibre Channel switch, will enable block-level storage traffic to be accessed
from a SAN over an IP network.
The iSCSI concept can be expanded to create a storage network by using
any network-connected device. iSCSI enables HBAs to provide I/O
processing on order to reduce the load on the server CPU.
Storage Area Networks - Conclusion
Benefits for SANs include
– Improved application availability
– Increased application performance
– Centralized storage
– Centralized management
SAN architecture and management are still evolving.
Emerging technologies such as FCIP and iSCSI are based on existing,
SANs components and technologies are being developed which will reduce
Management will continue to evolve with a goal of supporting a
heterogeneous multi-vendor SAN that would work with components from
Storage Area Networks - Bibliography
Introduction to Storage Area Networks,
http://www.redbooks.ibm.com/redbooks/pdfs/sg245470.pdf, March 2003
Windows Servers in a Storage Area Network Environment White Paper,
f28325805857/MS%20SANs.doc, April 2004
A Dictionary of Storage Networking Terminology: Common storage networking-
related terms and the Definitions applied to them, by the Storage Networking
The Emerging FCIP Standard for Storage Area Network Connectivity Across TCP/IP
Networks, http://www.snia.org/ipstorage/about/fcip/FCIP_whitepaper.pdf, June 2001
Storage Area Networks: An Essential Guide to SANs as a Component of Business
Continuation, by Mark Steinberg,
Storage Area Networks, http://www.saiitstorm.com/website3rd/storagenetwork.htm
Storage Networking with Fibre Channel& IP Networks,
http://www.iscsistorage.com/wp/papers/fcip.pdf, June 2004
Storage security: Emerging storage networking topic of interest,
http://i.i.com.com/cnwk.1d/html/itp/77_StorageSecurity.pdf, May 2004
Fibre Channel vs. SCSI: Which is more advantageous for your storage area network?,
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