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Fusion-io: SSDs are useless ... Let's build one

Developing super-speed SSD – SCSI Express accelerates SSD interface

After knocking SSDs for poor performance, Fusion-io is now building one itself – but throwing out existing speed-limiting SSD interfaces designed for disk drives.

A preview device, running at 95,000-plus IOPS, was shown at HP's Discover event in Vienna last month.

Fusion-io has criticised SSDs for poor performance, saying:

The power of SSDs is compromised when compared to memory acceleration options designed as a memory tier, such as PCIe-based flash memory cards. We are finding that PCIe solutions outperform SSDs by a wide margin

Producing its own SSD would be quite a turnaround, but this is what it appears to be doing.

Nigel Poulton blogged: "The concept box on display at Discover is an early prototype, but was an HP ProLiant server with an early Fusion-io 2.5-inch SSD drive connected to the PCIe bus (I know its not really a bus) via an SFF 8639 backplane connector (PCIe 12Gbps 6 lane). However, this is also do-able over PCIe cable implementations."

Poulton said: "They told me that the Fusion-io drive was literally only four weeks old."

He added: "It was a 2.5-inch hot pluggable drive. On the outside it looks just like any 2.5-inch SAS drive."

A Fusion-io spokesperson said: "The Fusion-io demonstration at HP Discover included a technology preview that integrated ioMemory technology with the emerging SCSI Express standard in an HP ProLiant server. Fusion-io is excited to continue working with others in the industry to evaluate the potential of these technologies."

Abandoning HDD interface paradigm for SSDs

This is not an SSD as we currently know it, a device with an interface designed basically for hard disk drives (HDDs).

Grant Jacobson, Fusion-io's director for HP alliances, wrote in his blog: "Connecting via the PCIe-based SCSI Express standard is consistent with Fusion’s cut-through architecture, which reduces latency and increases performance by moving data closer to the server CPU.

"Our HP Discover 2011 demo uses the same ioMemory and VSL technology as the recently announced Fusion ioDrive2 products, demonstrating the possibility of extending Fusion’s Virtual Storage Layer (VSL) software capabilities to a new form factor to enable accelerated application performance and enterprise-class reliability. "

VSL "allows file systems, volume managers, and applications to access flash through a common block interface. Similar to page tables in the host virtual memory subsystem, the VSL virtualises flash via 'block tables' and translates block requests to physical ioMemory addresses."

Host systems could use a Fusion-io PCIe flash card (ioDrive) or a Fusion-io SSD in exactly the same way: as a tier of host system memory underneath DRAM, and not as a faster chunk of external storage accessed through an interface designed to an HDD access paradigm.

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