Texas county puts IP SAN to work

The storage needs of the Denton County, Texas, appraiser's office were growing faster than its operating budget. So the appraisers took a chance on emerging storage technology based on the Internet Small Computer System Interface standard, or iSCSI.

The office offloaded some of its less-used data from Fibre Channel storage arrays to a less costly IP storage area network, while retaining most of Fibre Channel's fast performance.

'I didn't think iSCSI was mature enough for heavy database interaction, but it works fine for light interaction,' said Brad Green, head of the three-person IT department.

For several years, the Denton Central Appraisal District has been seeing tremendous growth in the volume of data it stores and serves up to citizens'about 300 percent per year, Green said.

The county itself is booming, thanks to its proximity to Dallas. According to the Census Bureau, the county has one of the fastest-growing populations in the United States, jumping by 5.3 percent from 2001 to 2002, to about 488,000 residents.

The appraiser's office oversees 300,000 residential and commercial properties. About 5,000 agents and other people routinely tap its data, including such large files as property maps and aerial imagery.

Moreover, uptime was crucial because police and fire departments sometimes use the appraisal data when responding to emergencies. Adding further strain was the county's recent decision to offer public information online, at www.dentoncad.com. Each year, residents have three months to protest property value reassessments, and they slam Denton's Web servers with database queries.

If the appraiser's office had had the budget, it could have added more units to its existing Fibre Channel SAN.

'We wanted to attach a lot of servers to centralized storage, but we couldn't afford to put fiber out to all of them,' Green said. 'The cost benefits of putting dual fiber cards in edge servers didn't really add up.'

Fulcrum Group, an integrator in Keller, Texas, suggested an IP-based SAN to supplement the Fibre Channel SAN.

Growing numbers of vendors are offering IP SANs using iSCSI. SCSI connectivity has long been used to link peripherals, such as hard drives, to computers. But iSCSI encapsulates SCSI commands in IP data packets that can be sent to other computers, letting them store data across networked devices.

Cheaper solution

IP SANs can be built from commodity networking equipment, which is far cheaper than hardware expressly for SANs. The storage commands can even work over existing LANs, eliminating the need for a separate storage network.

IP SANs can bring big storage savings to agencies willing to skimp a little in performance, said David Dale, chairman of the Storage Networking Industry Association's IP storage forum.

New Fibre Channel SANs boast 2-Gbps throughput, but most IP-based SANs use Gigabit Ethernet to carry traffic, with half the throughput. Vendors estimate that IP SANs cost about 20 percent as much as Fibre Channel networks.

Fulcrum set up demonstrations of then-new iSCSI SANs for Denton County, which tested IP SAN software from FalconStor Software Inc. of Melville, N.Y. It turned out to be difficult to integrate with the existing Fibre Channel SAN.

The county also tried a setup from Network Appliance Inc. of Sunnyvale, Calif., but decided against it because of a proprietary architecture and potentially high cost.

Finally Denton settled on Storage Concentrator i3000 from StoneFly Networks Inc. of San Diego.

The county now has 16T of combined IP and Fibre Channel SAN storage capability. It uses two storage concentrators and a CX600 Fibre Channel storage array from EMC Corp. of Hopkinton, Mass. The entire project cost about $1.2 million.

The mission-critical appraisal database resides on the Fibre Channel SAN, which is the most transaction-oriented, Green said. The IP SAN holds data such as backups, for which retrieval times aren't as stringent.

The IP storage network runs on a separate virtual LAN using a Cisco Systems Inc. Catalyst 4507 switch and a Dell Inc. 5224 switch under Microsoft Windows 2003 Server. Interfacing with the SAN proved to be a snap, as that version of the OS was the first with iSCSI initiators. The 7211C iSCSI cards came from Adaptec Inc. of Milpitas, Calif.

Green said he is pleased with the retrieval speed of the IP SAN.

'It's not as fast as Fibre Channel, but I've no problems with it,' he said. The county is now delivering geographic information system data to internal users over the IP SAN, with plans to transfer the GIS data to Fibre Channel later, 'but right now it is moving just fine,' Green said.

Setting up the IP SAN took considerably less time'two days to attach 10 servers'than the Fibre Channel SAN, which took a couple of weeks to connect to 10 servers, StoneFly officials said.

One reason is that IP SANs use standard networking technology understood by most administrators, whereas Fibre Channel requires specialized training.

'The IP SAN is much easier to use. I can farm out some of the IP SAN work to people who don't have SAN knowledge,' Green said.

About the Author

Joab Jackson is the senior technology editor for Government Computer News.


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