Looking to benefit from iSCSI storage?

Computer Technology Review, May, 2004 by Augie Gonzalez

Disk Servers: An Alternative Made Possible by Shrink-Wrapped Software

Like the name "database servers," the term "disk server" has been coined for a new class of storage devices that combine off-the-shelf PCs, general purpose networking cards and commodity disk drives with shrink-wrapped storage control software. The firmware functions buried inside a purpose-built storage array have been reimplemented in a portable form that runs on any standard PC, ranging from very low-cost, reasonably fast machines to moderately priced ultra highperformance systems. Just pick the storage service software options you require, then match the server hardware to the anticipated workload and capacity demands.

Head-to-Head Price/Performance Comparison

Industry standard benchmarks help users objectively measure the price/performance advantage of the disk server approach. In March 2004, the first SPC Benchmark 1 results for a disk server were published (www.storageperformance.org/results.html). At roughly half the price per SPC-1 IOPS than the nearest external array, a software solution harnessed the high power and low cost of a general-purpose server to set a new price/performance mark against conventional disk subsystems. That's an impressive advantage that will continue to get better as newer PCs, HBAs and disk drives become available. Next year, customers can take advantage of faster and cheaper platforms without waiting on vendors to incorporate those technologies into their arrays--at a much higher price.

The Technical Hurdle

Major breakthroughs were necessary to separate the embedded storage control software from the hardware. Creating an iSCSI target driver was just the beginning, made easier by LAN-ready servers with TCP/IP in the operating system. The real difficulty lay in implementing the entire collection of advanced storage control functions typically found on a high-end storage controller, including caching, LUN management, point-in-time snapshots, auto provisioning and remote replication. Arguably, only seasoned developers versed in high-end storage control have successfully maintained very high performance and complete software portability while coupling redundant disk servers to remove single points of failure. Such redundancy becomes paramount in mission-critical systems to ensure that disk servers take over for each other in the event of a hardware failure or a planned outage. But now all these capabilities can be found in products from leading storage ISVs.

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Disk server software is packaged in different ways. Generally, the products are structured in price tiers that correspond to the size of the environment and the types of features needed. This pay-as-you-go approach makes it possible to license the minimum software set required today then seamlessly add features and/or capacity when the upgrades are needed. One might start with the entry-level iSCSI implementation and later introduce the snapshot feature. Some offer Fibre Channel host connections alongside the iSCSI ports for higher, more deterministic I/O performance required by larger hosts.