If a vendor claimed to offer a storage-area network (SAN) with the performance of Fibre Channel (FC) but without the cost and complexity, jaded FC administrators might be a hard sell. After all, FC network devices have been notoriously incompatible, expensive and complex to administer.
But IP SANs promise to change all that by implementing the Internet Small Computer Systems Interface (iSCSI) protocol, which enables SANs to operate over industry-standard TCP/IP and Ethernet.
The concept of storage networking over IP isn't new: Network-attached storage appliances have long delivered file services over IP using Network File System or other file-sharing protocols. But creating storage networks that allow highly efficient block-level transfers between application servers and shared storage pools has been the domain of FC networks—a switched, high-speed serial interconnect requiring specialized cabling, host bus adapters (HBA), switches and management software.
IP SAN architecture, an extension of existing SCSI and TCP/IP Ethernet standards, could reduce costs by creating a unified corporate IP network that's easier to design, integrate and manage than a traditional FC SAN. ISCSI networks are also compatible with IP-based security mechanisms such as Kerberos, public-key encryption and IPsec.
Setting up an IP SAN isn't simply a matter of plugging in iSCSI-attached storage, however. While an IP SAN can run on standard Gigabit Ethernet switches, the overhead involved in processing of TCP and iSCSI protocols can quickly overwhelm the CPU in servers with significant storage network traffic. IT managers may need to replace standard Ethernet adapters with special HBAs called TCP off-load engines (TOE).
John Flynn, IT director at Minneapolis-based NRG Energy Inc., says he hopes to get by without TOEs. "None of [our] applications have high-performance I/O requirements," he says.
But Rick Halbardier, project coordinator for Washau County, Nev., will need TOEs for the IP-based tape backup SAN he's testing. "Backups tend to use all the CPU resources available to the system," he says.
Halbardier is optimistic about the emerging TOE adapters. But, he says, "I don't know that we can say it's going to be reliable until we've tested it."
It might not be compatible, either. Standards committees are hammering out iSCSI draft standards (the final version is expected this summer), but vendors are rushing products to market. There are no standards for TOE, different vendor interpretations of the iSCSI standard could lead to interoperability problems, and no certification process exists. And vendors have little credibility in the user community after the interoperability debacle with early FC devices.
Once the standard is stable, analysts predict, IP SANs will slowly replace FC, but users with an investment in FC are unlikely to change over soon. "You don't replace existing technology with emerging technology," says Dan Tanner, an analyst at Aberdeen Group Inc. in Boston, adding that FC now supports 2G bit/sec. speeds while Ethernet still maxes out at 1G bit/sec.
Initially, the best fit for iSCSI may be around the edges of the FC SAN, where its lower cost makes more sense. But early adopters might do well to emulate Flynn's pragmatic approach to IP SANs. By choosing FC storage arrays with an FC/iSCSI switch, he can move to FC if things don't work out.
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Q&A
The Benefits Of Storage Over Ethernet
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Ahmad Zamer, chairman of Storage Network Industry Association's iSCSI subgroup |
Ahmad Zamer, product line manager at Intel Corp.'s LAN access division in Austin, Texas, is chairman of the Storage Networking Industry Association's iSCSI subgroup. He recently talked with evaluations editor Robert L. Mitchell about the iSCSI protocol.
What is iSCSI good for? The main concept of iSCSI is to allow people to build storage-area networks using Ethernet. If you already have a large network that is built around Ethernet, it is natural to connect the storage to that network rather than having to learn new ways to deal with storage. Smaller and medium-size organizations cannot afford the cost of Fibre Channel SANs. We expect iSCSI to be cheaper and easier to implement.
What are the immediate benefits? The main benefit is the long operating distances that iSCSI will bring to the table. Right now, you have to jump through a lot of hoops to put your storage far away for disaster recovery. IP storage makes it doable.
When will the standard be final? We will create the document [this month], and it goes into a three-month review period. Then we go into the July or August meeting and expect that we will get out with a standard.
Does "standard" really mean interoperable? We want to make sure products interoperate. We do not want to see the consumers get stung again by another untested set of products that the vendors say are OK but when plugged in don't work together.
How will costs compare to FC? Lower training, lower cost of ownership. The management costs will be cheaper in terms of management tools and human resources. As the product matures, you'll be able to manage the network from one window.
Who should skip iSCSI? Where you do not need [iSCSI's] operating distances and you have already invested in FC, there is no point at this moment to switch to iSCSI.
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Get Ready for IP SANs: Did Someone Say 'Standards?' online exclusive IP Storage Products and Vendors online exclusive Nishan's Clark: iSCSI vs. Other Protocols online exclusive Payoffs and Pitfalls of iSCSI online exclusive |
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