iSCSI SANs: Better and cheaper?

Hossein Shahrokhi is adding 20 servers to his Fibre Channel storage-area network (SAN) at the University of Houston-Downtown. But Shahrokhi, executive director of IT, isn't laying new fiber-optic cable runs, buying expensive Fibre Channel switches or installing Fibre Channel host bus adapters in his application servers to make this happen.

Instead, he's using a special network switch that converts the Fibre Channel protocol to iSCSI, an emerging standard for creating SANs that run over TCP/IP Ethernet networks. Shahrokhi hopes to use iSCSI (pronounced "eye scuzzy") technology to create an IP SAN that uses his existing Gigabit Ethernet adapters, switches and copper network cabling. With Fibre Channel, he says, "we were looking at $1 million" to acquire the technology. "With this approach, I can do this reasonably for $250,000."

The iSCSI draft standard won't be final until this summer, and its reliability, performance and interoperability are as yet unproven. But as this technology evolves, lower equipment costs could be just one part of the potential savings. IT may also save by using existing IP network support staff to manage IP SANs, rather than hiring expensive Fibre Channel technicians. And the support staff may be able to use existing IP-based network management tools as well, simplifying not just the network, but also its management and support.

SAN Evolution

SANs create a network-attached storage pool that's directly addressable by application servers over a dedicated high-speed network. They move data in block format -- the way SCSI storage devices actually read and write data -- rather than as discreet files. This approach allows for more efficient data transfers and the ability to consolidate and better manage storage resources.

Traditional SANs run on a 1G bit/sec. or 2G bit/sec. fiber network using the Fibre Channel protocol. But Fibre Channel SANs are expensive to build, have a working range of 1 kilometer, and require specially trained personnel to run, so most don't extend beyond the data center. By contrast, an iSCSI SAN can run over existing 100M bit/sec. or 1G bit/sec. Ethernet networks and can be used to connect distant offices. And since most networks use switched Ethernet, existing network cabling can be easily segmented to accommodate storage network traffic.

Vendors are rushing to market with early iSCSI devices. IBM is already shipping a native iSCSI storage array. Cisco Systems Inc. and Nishan Systems Inc. in San Jose offer Fibre Channel-to-iSCSI switches for attaching Fibre Channel storage or linking Fibre Channel and iSCSI SANs. And Adaptec Inc. and Intel Corp. are building iSCSI host bus adapters (HBA), which are designed to optimize iSCSI performance on servers and iSCSI storage devices.

Should You Buy In?

Possibly. Most analysts expect iSCSI to eventually replace Fibre Channel, but there's no bottom-line benefit to replacing an existing Fibre Channel SAN today. However, iSCSI can be useful in smaller, departmental situations where a Fibre Channel investment doesn't make economic sense, or for niche applications, such as remote backup using iSCSI's highly efficient block data transfer capability. Small-scale pilot projects such as these will allow IT staff to gain experience with iSCSI and Internet Protocol storage networking early on, paving the way for a smooth transition as the technology matures.

The following are key factors that will affect ROI:

Infrastructure Costs

"The capital expense and operating expense [of iSCSI SANs] should be a lot less," says Dan Tanner, an analyst at Boston-based Aberdeen Group Inc. But the prospective upfront cost savings depend on your current network infrastructure and could be a wash. For example, most IP SANs will require a Gigabit Ethernet backbone for adequate performance. If an iSCSI SAN can use existing IP switches, you'll save at least $20,000 on Fibre Channel switch costs. But if you're attaching Fibre Channel storage devices or interconnecting Fibre Channel and iSCSI SANs, you'll need special switches, such as Cisco's $27,000 SN 5420 multiprotocol storage router.

Technically, although a server with any Ethernet adapter can access an iSCSI SAN, the processing overhead associated with the TCP and iSCSI protocols can quickly bog down a server CPU as storage traffic mounts. You'll probably need to buy HBAs that off-load TCP and iSCSI processing. Initial prices for these adapters will rival those of Fibre Channel HBAs, which typically run $750 to $1,000. Prices are expected to drop quickly to perhaps half that as competition heats up.

It's true that you don't need to run fiber-optic cable for iSCSI. But most servers on a SAN have two or more storage-network adapters for redundancy and performance, and most iSCSI HBAs don't support regular network traffic. (One vendor, San Jose-based Alacritech Inc., offers an HBA that supports both traffic types.) So, IT may still need to pull copper cable for at least two additional cable runs -- and it may also need to add extra Gigabit Ethernet switches.

As they did with Fibre Channel, vendors are rushing products to market ahead of the standard. And, like Fibre Channel, early iSCSI devices may not be interoperable, which will likely require device-driver or flash ROM upgrades that result in service interruption -- something to avoid on a storage network.

Theoretically, IT should be able to manage iSCSI storage networks using existing IP-based enterprise network management tools. But tools to manage high-level SAN functions such as mirroring of storage for rapid disaster recovery, or remote copying for backups, will likely require additional software investments when they become available.

Easier Management

The greatest return on an IP SAN investment may come from operational and human resources cost savings associated with a simplified network infrastructure. "Our goal is to minimize the number of technologies we support, and integrate the skill sets as much as possible," says Shahrokhi. ISCSI may help him move toward the ideal of having one set of network management tools, and one support group that can handle servers, networking and storage.

"For most IT managers, what's closest to their heart is ongoing support and people," Shahrokhi says. In the Houston area, Fibre Channel experts cost $80,000 to $100,000 per year --- if you can keep them, he says. But if you build an iSCSI infrastructure, don't expect those savings to go right to the bottom line. "Just because you have IP people doesn't mean you have a storage person," says Steve Duplessie, an analyst at Enterprise Storage Group Inc. in Milford, Mass. Additional cross-training or staffing may be needed, whether for IP or Fibre Channel storage networking.

So, How Do You Measure Payback?

While iSCSI technology shows early promise, the best way to establish ROI may be to implement small pilot projects outside the data center. That would give IP network support staff the opportunity to begin climbing the IP storage learning curve -- and the technology can begin proving itself in the real world.

Copyright © 2002 IDG Communications, Inc.

  
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