Special Supplement: iSCSI: Low-cost alternative to FC


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Storage August 2006 Special Supplement


Components of an iSCSI SAN

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iSCSI initiator: The host-side endpoint of an iSCSI session. iSCSI initiator software runs on the operating system or in an iSCSI host bus adapter (HBA) to communicate with an iSCSI target.

TCP/IP Offload Engine (TOE): A PCI or PCI-X adapter that offloads TCP/IP processing from a server's CPU. With TCP/IP overhead less than 10% for 1Gb/sec sessions, TOEs will become more important with 10Gb/sec Ethernet.

iSCSI HBAs: A PCI or PCI-X adapter that offloads TCP/IP and iSCSI processing. iSCSI HBAs typically provide an on-board iSCSI initiator and have been required to boot from iSCSI storage.

iSCSI target: The endpoint of an iSCSI session. Examples of iSCSI targets are storage arrays, tape drives and iSCSI gateways.

Ethernet switches: Standard Ethernet switches connect clients running iSCSI initiators and iSCSI targets.

iSCSI gateways: Multiprotocol routers that support iSCSI and Fibre Channel (FC); mainly used to provide access to back-end FC storage via iSCSI.

The iSCSI product landscape
iSCSI target vendors can be grouped into three categories: pure iSCSI players, traditional storage vendors adding iSCSI support to their existing arrays and iSCSI gateway vendors (see "Components of an iSCSI SAN," at right).

Among the pure iSCSI players are iSCSI pioneers EqualLogic, Intransa, LeftHand Networks, StoneFly and Sanrad Inc., as well as younger startup companies such as Nimbus Data Systems Inc. Most offerings in this group are running iSCSI target software on a server--in most cases concealed in an appliance form factor--with attached storage and some flavor of a general-purpose OS. Vendors in this category have added storage features previously available only in FC SANs, including snapshotting, remote replication, load balancing and virtualization, which enables them to compete head to head with FC vendors.

Traditional storage array vendors such as EMC Corp., Hewlett-Packard (HP) Co., Hitachi Data Systems and Network Appliance (NetApp) Inc. have added iSCSI support to their arrays to more effectively support their large customer bases. "EMC is protocol-agnostic and supports FC, iSCSI and NAS ... enterprises run more than one protocol," says Ken Steinhardt, EMC's chief technology officer. Conspicuously absent from the list is IBM Corp., which hasn't added iSCSI support to its high-end arrays. With the exception of the low-end TotalStorage DS300, IBM depends on its partnership with NetApp to fulfill higher end iSCSI customer requests.

"If the demand for iSCSI increases at the higher end, IBM will respond to the market demand," says Craig Butler, IBM's brand manager for midrange storage products.

Similar to large array vendors, FC switch vendors Brocade Communications Systems Inc., Cisco Systems Inc. and McData Corp. have either added iSCSI support to some of their FC switches or are offering dedicated iSCSI gateways to enable enterprise customers to attach iSCSI servers to existing FC storage.

"By adding iSCSI support to our MDS 9000 series directors and switches, we enable midrange and workgroup servers to inexpensively connect to FC storage," says Rajeev Bhardwaj, product management manager for Cisco's data center and storage technology group.

This was first published in August 2006

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