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Storage Area Networks (SAN) Technologies

Storage Area Networks (SAN) Technologies

Fiber Channel and IP (iSCSI)
The two access methods available for SANs are fiber channel and Internet Protocol (iSCSI).

Dedicated fiber-channel networks attach servers to storage devices. The fiber- channel network passes data blocks around (blocks are used by disk access), which the servers access through host-bus adapters. The servers then attach to LANs to provide the information to the rest of the network. SAN components include host-bus adapters, storage systems (RAID, JBOD, tape, and optical disk), hubs, switches, and SAN-management software.

Fiber channel is an American National Standards Institute (ANSI) standard that combines both channel and network technologies. SCSI and iSCSI are the primary upper-layer protocols available on fiber channel. Fiber channel operates at gigabit speeds.

You can use several topologies for fiber-channel deployment:

  • Point to point ' Dedicated connections between a server and storage device. This method is suitable when storage devices are dedicated to a single file server.
  • Arbitrated loop ' Storage and file servers connect to each other in a closed loop with up to 126 nodes. Maximum bandwidth is 100 MB shared between all the nodes. Therefore, the number of attached nodes directly affects the performance of the loop.
  • Switch fabric ' As with Ethernet, performance and reliability vastly improve when moving from shared media (such as an arbitrated loop) to switched fabrics. A fiber-channel switch offers up to 100 MB to each switched port. You can trunk switches together to attach up to a theoretical 16 million nodes.

SAN addresses these issues by doing the following:

  • Reducing management costs through centralized control for monitoring, backup, replication, and provisioning.
  • Reducing subsystem costs through any-to-any connectivity between storage and servers. This setup allows networks to match servers with underutilized storage subsystems.
  • Reducing backup costs through the centralization and consolidation of backup functionality.
  • Offering highly available disk services by providing redundant, multiple paths between servers and storage devices. This provision allows for automated failover across all storage in an easily scalable manner.
  • Offering highly scalable and location-independent disaster recovery. You can replicate entire data centers to multiple locations, allowing quick and efficient switchover if the primary data center becomes unavailable. DAS networks are unable to provide this level of disaster recovery.

The other access method to fiber channel is IP (iSCSI).
Because SANs connect to IP networks, the storage can be accessed across LANs, WANs, metropolitan-area networks (MANs), and the Internet. You can manage the devices using Simple Network Management Protocol (SNMP) and operate in a secure mode with the use of Internet Protocol Security (IPSec), firewalls, and virtual local-area networks (VLANs). Storage devices can connect to Ethernet devices.

Whereas fiber channel separates disk-block'based traffic from the rest of the network, IP-based SAN tunnels block traffic through the IP network using the Internet Protocol SCSI (ISCSI) protocol. ISCSI uses Transmission Control Protocol (TCP) as its transport.

Internet Small Computer Systems Interface (iSCSI)
iSCSI (pronounced “i-scuzzy”) is a method of encapsulating SCSI data and command frames into IP packets, enabling universal access to storage devices and SANs over standard TCP/IP networks.

Fiber channel over IP (FCIP) is another technology that allows fiber-channel networks to connect to each other over LANs, MANs, and WANs. FCIP uses TCP to tunnel fiber-channel block traffic across the IP network.




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