Solid boost to I/O speed

FRAMINGHAM (09/25/2003) - The Unisys Corp. mainframe at Greater El Paso's Credit Union had run out of steam. Response times had slowed to unacceptable levels as transaction volumes climbed to 135,000 per day, and completion times for nightly batch-processing jobs stretched to seven hours. Meanwhile, new regulations forced the credit union to keep systems online longer, leaving only a six-hour window to complete those jobs. "We needed to do it faster," says Rudi Kuehne, senior vice president of data processing.

After identifying database I/O as the bottleneck, Kuehne upgraded to an EMC Corp. Clariion storage array. That helped, but the problem didn't go away. "Even with faster disks, we didn't gain enough time to satisfy the operational requirements," he says.

Kuehne considered replacing the entire mainframe but instead spent US$219,000 earlier this year on a solid-state disk (SSD) appliance from Texas Memory Systems Inc. in Houston. By moving key database files onto the 32GB device that functions as a giant RAM disk, the credit union cut per-transaction response times from 0.6 to 0.35 seconds. Nightly batch-processing times dropped to four hours. "This saved us from spending $2.5 million on a new mainframe," he says.

Prices are falling

SSD devices have been around for more than 25 years, but high costs have kept them out of most data centers. However, as the cost per megabyte has plummeted relative to traditional disk storage, SSD appliances have found limited acceptance in areas such as online transaction processing and video editing, where extreme disk I/O loads may outpace even very fast storage arrays.

SSD has several benefits, says Peter Gerr, an analyst at The Enterprise Storage Group Inc. in Milford, Mass. "It delivers excellent performance. It is nonmagnetic. There are no rotating components, so there is very low latency," he says. SSD access times range from 0.01 to 0.1 msec vs. 4 to 10 msec for the most advanced, 15,000-rpm disk drives.

But despite declining costs, SSD technology is still expensive compared with rotating disk systems. SSD appliances average about $1.85/MB, whereas disk prices range from 2 cents/MB for low-end Advanced Technology Attachment (ATA) devices to about 7 cents/MB for high-end EMC Corp. storage arrays, Gerr says. Low-end SSD appliances start at about $3,000, and high-end models with 1TB of storage can run well over $1 million.

Since there are no moving parts, SSD systems are very reliable, and all products offer the same basic features. They use synchronous dynamic RAM, support data mirroring between banks of memory and include a backup battery and a hard disk onto which the system can automatically write the RAM disk contents in the event of a power failure. "It is the integration of the components that is the differentiator, and the software they offer," Gerr says.

Tech for Many Tasks

Vendors claim their appliances can do everything from expanding the number of user sessions a single Citrix Systems Inc. MetaFrame server can support to speeding up e-mail system performance and restoration times. For example, Solid Data Systems Inc. in Santa Clara, Calif., offers high-speed recovery software for Microsoft Exchange servers. TiGi Corp. in Vienna, Va., offers hybrid RAID/SSD appliances and software that allows for snapshot backups of the RAM disk contents. And Texas Memory Systems stripes data backups across three hard disks in its appliance to allow continuous trailing backups of RAM disk contents.

Despite these features, few end users are aware of SSD, says Gerr. "In the financial industry, it's pretty well known. Outside that, it's in an early-adopter phase," says Woody Hutsell, executive vice president at Texas Memory Systems. And only a handful of small vendors offer the appliances, which caused concern for Kuehne, who was looking for a stable vendor with enterprise-class support. "After some soul searching, we decided that it was worth the risk," he says, adding that he checked the vendor's financial viability before proceeding.

Stability also worried Mark Flieger, vice president of information services at Hingham, Mass.-based health care provider Occupational Health + Rehabilitation Inc., which put the transaction logs for its disk-bound SQL Server database on a $20,000 SSD appliance from Platypus Technology Inc. in North Billerica, Mass. He says the system's redundancy and the ability to move operations to disk in the event of failure convinced him to take a chance.

The limited number of SSD deployments also means that the appliances haven't been tested with many systems. "I would ask, 'Can this device coexist with my other systems, or will it just increase the complexity of my environment?' " says Gerr.

In Kuehne's case, the system didn't work with his mainframe, even though both Blue Bell, Pa.-based Unisys Corp. and Texas Memory Systems had said it would. "We were told it was certified to run on (Unisys) mainframes, but it had never been certified on our model," he says. The Unisys system interface wasn't designed to accept data at RAM disk speeds and timed out. The two vendors eventually remedied the problem with a microcode update for the Unisys hardware, but the process kept the system off-line for six weeks.

Who Needs It?

Charles Miller, senior vice president of data center engineering and operations at KeyCorp in Cleveland, dismisses SSD as unnecessary. "Originally, solid-state storage was necessary for critical high-access data sets for online transaction-processing systems," he says. "The response time provided by traditional direct-access storage devices (DASD) created performance bottlenecks for these applications. In the last five years, the performance increases in traditional DASD with large cache sizes has mostly eliminated the need for solid-state storage."

Gerr doubts that the technology will move into the mainstream anytime soon. "It just doesn't have the economic fundamentals," he says. But SSD appliances have their place in the data center, particularly for transaction-intensive applications where random data-access patterns make the system "cache-unfriendly," he says. "If you have that demanding of an application, and traditional storage solutions haven't provided the performance you need, then you might try (SSD)," Gerr says.

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