IBM boosts SVC, but is it enough?

SVC Version 3.1 will support up to four times more servers than the previous version, but its limited throughput may still present a problem for users in the largest environments.

IBM announced an upgrade this week to its SAN Volume Controller (SVC) storage virtualization software that will allow it to support more servers. But analysts say the throughput performance may still not be enough for performance-intensive environments.

SVC is a collection of eight cluster nodes in pairs called I/O groups. Each node, in the past, supported two I/O groups, and the software could attach up to 256 servers. The new version supports four I/O groups per node, scaling up to support 1,024 host servers and up to 4,096 virtualized disks.

The cache memory in SVC Version 3.1 was also doubled, up to 8 GB, and I / O per second (IOPS) was increased , according to preliminary benchmark testing, from 100,128 IOPS to roughly 150,000. IBM said the official testing results have yet to be published and an exact number is not yet known. The improved performance, they said, is due to the use of a faster processor in the SVC appliance as well as the improved memory.

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"This is great from a simple scaling standpoint," said Greg Schultz, analyst with the Evaluator Group. "However, users should be careful when simply adding more servers without regard to performance. Even though IBM has quadrupled the number of attached supported servers, the performance has only increased by a factor of 1.5 over previous versions. For I/O intensive environments, the math might not quite balance out."

Another performance complaint from the previous iteration of SVC was that I/O was not balanced between nodes -- IBM declined to address this issue.

Meanwhile, rumors remain widespread that IBM will soon OEM software from a startup called Incipient Technologies Inc. in order to offer a better-performing, switch-based virtualization product.

SVC currently runs on Cisco Systems Inc. switches, but acts like a storage controller in such an implementation, using its cache to process every I/O to the back-end servers and arrays. This is different from EMC Corp.'s Invista virtualization switch, which allows I/Os to be sent directly to the underlying storage system, focusing only on advanced operations like snapshots and mirroring. Thus, Invista doesn't have to have as much cache as it isn't controlling the entire storage infrastructure, and therefore achieves better throughput on specific tasks.

According to industry scuttlebutt, Incipient's software could give SVC the functionality boost it needs. The company's official Web site states that it has "a relationship" with Brocade Communications Systems Inc. and that it will announce more partnerships in the coming months, but both companies have remained tightlipped as rumors have flown.

Right now it seems that not everyone in IBM's market needs Invista-like functions. Lyle Gleason, storage architect with the city of Richmond, Va., said that he is satisfied with the performance of the current SVC in his 120-server shop, and that he plans to upgrade to Version 3.1 only because he knows IBM will eventually stop supporting the older version.

"But it's great that they're adding support for much larger infrastructures -- it shows that virtualization is on everyone's minds," he said. "IBM might be missing an opportunity if they didn't provide that functionality."

"Invista works for people working to isolate servers from storage devices to perform migrations in larger environments where they're continually reconfiguring and making changes," Schultz said. "They could benefit by having a virtualization layer between servers and storage while still using the functionality that comes with their storage systems.

Intelligent switches have a lot of horsepower down at the chip level, according to Brian Garrett, director of Enterprise Strategy Group Labs. "IBM might be looking the same way if intelligent switches took off and people switched from application-based virtualization. But that market will still take a couple years to mature," he said.

"It's still just a rumor, but it wouldn't surprise me if they did develop the product, looking at IBM's portfolio," Schultz said. "They have lots of products that coexist in the same space."

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