What you will learn from this tip: ISCSI arrays will save you a pretty penny, but at a slight cost in terms of performance.
For small and medium-sized businesses, iSCSI arrays offer good-enough storage at a compelling price point. But there are a few disadvantages to consider.
ISCSI arrays, like iSCSI SANs as a whole, promise low initial cost and a familiar Ethernet environment, albeit while offering lower performance than Fibre Channel. Right now, further disadvantages include the uncertainties of a new technology, relatively few vendors in the space and tools that are still maturing.
The drives on an iSCSI array don't speak Ethernet themselves. They are standard drives, either SCSI or SATA. A controller handles wrapping and unwrapping the data packets for transmission over Ethernet. This simplifies provisioning and replacement of drives considerably.
ISCSI SANs are aimed at small and medium-sized businesses and the arrays reflect that -- both in terms of capacity and pricing. For example, IBM's new TotalStorage arrays Model DS300 and DS400 are almost identical except the DS400 is a Fibre Channel array and the DS300 is iSCSI. The DS400 sells for between $5,000 and $7,000 and handles up to 5.8 TB of storage. The DS300 only costs $3,000 to $4,600 and tops out at 2 TB. The capacity scale is a matter of marketing rather than technology: IBM's discontinued 200i iSCSI array could handle up to 3.5 TB of storage.
Most currently available iSCSI arrays max out at 2 or 3 TB, while some can support up to 5 TB. A few products, like the EqualLogic Peer Storage Array, can support multiple SCSI RAID arrays with up to 110 TB of raw capacity. If you want larger iSCSI arrays you can use an iSCSI gateway in front of a conventional RAID array.
Generally speaking, current iSCSI array users will find the widest selection of products in they stay in under 3 TB range.
For more information:
Tip: How to tweak Ethernet for iSCSI SANs
Tip: Pound-foolish iSCSI: Should you use NICs in SANs?
About the author: Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years, he has been a freelance writer specializing in storage and other computer issues.