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Debate on flash memory's future heats up

Posted: 08 Sep 2008 ?? ?Print Version ?Bookmark and Share

Keywords:flash? storage? PCIe? SSD?

Storage gurus from IBM Corp. and EMC Corp. spent much of last week debating the future of flash memory drives in servers and storage systems. In a candid online exchange, the two agreed flash drives will rewrite the rules for system storage, but took significantly different views on how to implement solid-state disks (SSDs) in servers.

The debate launched last week when IBM announced it had worked with startup Fusion-io, a flash controller designer, to hit a sustained data transfer rate of more than one million I/O operations/second (IOPS) with a response time of less than a millisecond. The Fusion-io controller uses PCIe, unlike most flash drives that use the serial ATA interconnect popular on hard drives.

Barry Whyte, a senior IBM storage designer, posted a detailed description of the IBM work called Project Quicksilver. In his posting, Whyte took a few swipes at competitor EMC. "Although EMC was early to call the significance of flash drives, it plugged SSDs from Step Inc. into its existing systems rather than take IBM's approach of designing a more optimal platform for flash," he said said.

Pros, cons
The posting attracted a mixture of kudos and criticisms from Barry Burke, chief strategy officer in the Symmetric group at EMC and an avid blogger on storage technology. "Congrats on the accomplishment and thanks for joining in the efforts to make flash a commercial reality," wrote Burke.

However, he and other EMC technologists were also quick to probe some aspects of the IBM milestone. They noted that PCIe cannot support the RAID features that typically provide storage redundancy, and they questioned whether the million IOPS could be sustained when all storage management features were in use.

Burke noted that IBM has yet to fully describe the test system that uses more than eight processors. Although IBM has published performance from earlier tests updated in March, it has not been able to document the million IOPS milestone because it was achieved on an unreleased system.

Whyte admitted the Fusion-io card does not support RAID. However, he said, IBM has developed a version of its virtualization software that handles disk mirroring for flash controllers and allows hot swapping of cards if a failure occurs.

Whyte also shared running all storage management features can slow performance and increase CPU functionality. However, he said the test system had plenty of processing overhead.

Seeking symmetry
Both sides agreed that balancing the uneven read and write performance of flash drives is one of the challenges to integrating SSDs in servers. "There are ways to mitigate those issues with a little bit of old-fashioned innovation and some integration between the drive and the array microcode," Burke said.

"In general, most companies are simply plugging SSDs into existing serial ATA interconnects buses for hard drives," noted Whyte. He said IBM, Intel and Sun are experimenting using PCIe and DIMM connections.

"But the best approach is to build a storage controller that is truly optimized for this game changing technology. That's what we have prototyped," he stressed.

- Rick Merritt
EE Times

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