Special Supplement: iSCSI: Low-cost alternative to FC


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Storage August 2006 Special Supplement


iSCSI boot from SAN not so easy

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One of the shortcomings of iSCSI has been the inability to boot from iSCSI-attached storage through a regular network interface card (NIC). The boot process is performed by the system BIOS and with the iSCSI software initiator running at the OS level, iSCSI storage is out of reach until the OS has booted. The only practical solution in the past was adding an iSCSI host bus adapter from companies like QLogic Corp., which provides the interrupt 13 (INT13) extensions required for booting, as well as an on-board iSCSI initiator.

This changed in April when Microsoft Corp. announced support for software-based SAN boot of Windows using the Microsoft iSCSI Software Initiator and standard NICs through a technology co-developed by Microsoft and IBM Corp. Software-based SAN boot requires a NIC firmware upgrade or an upgrade of the System Options ROM of blade servers.

Although the Microsoft announcement is a big step forward, iSCSI boot still requires a dedicated LUN for each server. "Microsoft is looking into a single-boot image solution that allows multiple servers to boot from a single LUN, but this is post-Longhorn," says Claude Lorenson, Microsoft's group product manager for storage. For a single Windows boot image to become reality, Microsoft needs to eliminate System Identifiers (SIDs), rework Windows licensing and possibly eliminate the notorious registry. The upside, however, is huge: Multiple systems booting from a single LUN will let corporations extend iSCSI-to-desktop computers and eliminate DAS by booting desktop computers directly from an iSCSI SAN.

Trends and developments
One could argue that the popularity of NAS was the main reason for the ever-increasing interest in iSCSI. NAS dependency on higher level file-system protocols (CIFS/NFS) makes NAS less suitable for block-based transactional applications like databases; as a result, NAS vendors are adding iSCSI support to their offerings. Because NAS and iSCSI are both based on TCP/IP, iSCSI is a more natural SAN supplement than FC in NAS environments.

NetApp provided iSCSI support for its filers after iSCSI was ratified, and has been a staunch promoter ever since. Microsoft will release a Feature Pack for Windows Storage Server 2003 R2 this summer to make its NAS an iSCSI target through WinTarget software acquired from String Bean Software. And EMC's Multi-Path File System for iSCSI lets the Celera NAS use iSCSI to return a NAS request, resulting in a big performance boost for large file requests.

The number of innovations and companies developing for the TCP/IP and iSCSI space today greatly surpasses the number of FC developments. Besides 10GigE, network packet processors--from companies like Broadcom Corp. and Cavium Networks--for packet inspection, prioritization, encryption, compression and TCP optimization are the building blocks for next-generation TCP/IP and iSCSI products.

An example of the high level of innovation in the networking space is Broadcom's development of 2.5Gb/sec Ethernet components that support 1Gb/sec and 2.5Gb/ sec Ethernet on a part-by-part basis. The 2.5Gb/sec Ethernet components are targeted mostly toward blade servers, enabling blade-server vendors to offer transparent upgrades of server blades to 2.5Gb/sec Ethernet, resulting in a 2.5 times performance boost. Unlike 10Gb/sec, 2.5Gb/sec Ethernet allows leveraging of existing backplanes and cabling.

There's no doubt iSCSI will dominate the SMB storage space and will be the preferred storage option for workgroup servers and, eventually, corporate desktops (see "iSCSI boot from SAN not so easy," this page). What's still unclear is if iSCSI can push FC out of the enterprise data center. With FC's large installed base, long-standing support for mission-critical apps and the availability of 8Gb/sec FC, it's the preferred technology for most large data center storage. For a transition to happen, it will take large storage vendors like EMC, HP and IBM to recommend iSCSI over FC, which is unlikely to happen in the near future.

This was first published in August 2006

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