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OCZ's HSDL: A New Storage Link For Super-Fast SSDs

So, the interface is one part of today’s story. The HSDL-compatible drive is the other.

For all intents and purposes, the technology underlying HSDL is completely transparent to the enthusiast or IT administrator that sets it up. Plug in the controller card, attach the SFF-8087 connector to the 3.5” drive, plug in a SATA power cable, install the Silicon Image drivers and go.

But I couldn’t resist dismantling the thing.

Inside the IBIS, you’ll find three boards. There’s one controller board hosting the SAS/power connections and a 3 Gb/s Silicon Image SiI3124 PCI-X-to-four-port-SATA controller, which snaps into an internal backplane. Two other boards are loaded down with 34 nm MLC NAND from Intel, along with a pair of SandForce SF-1200 controllers each. Each one of these appears as a 55 GB drive in the Silicon Image controller BIOS.

Silicon Image four-port SATA 3Gb/s controllerSilicon Image four-port SATA 3Gb/s controller

If it helps, think of the IBIS as very similar to the RevoDrive X2 that SandForce was showing off at IDF 2010. Only, instead of dropping into a PCI Express x4 slot, the IBIS plugs into a controller that drops into a PCI Express x4 and communicates over an interface that is in no way throughput-constrained today. Architecturally, though, both drive products are really very similar.

Of course, the IBIS is bootable, and although Windows 7 doesn't include the driver for Silicon Image's controller, adding once Windows 7 setup reports that it didn't find any drives lets the OS see the SSD and install to it. Although there are 256 GB worth of NAND chips and OCZ advertises our sample as a 240 GB offering, you actually get 223 GB of usable space. This is a result of 1) a binary to decimal conversation and 2) over-provisioning on OCZ's part.

SandForce SF-1200 controller (x4)SandForce SF-1200 controller (x4)

The sample OCZ sent over boasts 128 GB of flash per board (256 GB total), though the drive’s advertised capacity is 240 GB. In essence, what you’re getting is an array of 128 GB flash-laden boards inside that 240 GB model. Technically, this isn’t actually RAID 0; OCZ employs Frame Information Structure (FIS)-based switching, allowing the Silicon Image IC to talk to all four SandForce controllers simultaneously and facilitating the aggregated bandwidth you’d normally chalk up to striping. Presumably, the lower-capacity drives don’t employ as many channels per board, resulting in performance figures that trail the 240-960 GB SKUs. OCZ’s data sheet claims maximum sequential reads of up to 740 MB/s and writes as high as 690 MB/s, with up to 100,000 IOPS for the 100 and 160 GB drives.

Source: SATA-IOSource: SATA-IO

OCZ does have plans to sell a separate RAID card that’ll allow you stripe physical drives together—the board needs another logic chip to mux/demux the drives’ channels. The company knows that there are certain features that’ll need to be enabled if it hopes to see widespread adoption, and it says they’re being worked on currently. RAID support is one of those features. S.M.A.R.T. compatibility is another.

The IBIS drives don’t support TRIM in any form today. OCZ claims that this could potentially change in the future, but assume it won’t if you’re shopping around today. OCZ also makes no mention of idle garbage collection support, though past experience suggests this shouldn’t be a serious issue on a SandForce-based product. Should we experience performance degradation after prolonged use, we’ll make an update to this piece. Update: I followed up with OCZ, and it sounds like the SandForce controllers perform their own form of garbage collection, wrapped up into the DuraClass technology package. This should help maintain the drive's performance.

One side of one storage board inside the IBISOne side of one storage board inside the IBIS

Also, be sure you’re dropping the IBIS into a system with ample system throughput. Naturally, using the drive on a P55-based platform already rocking a discrete graphics card is going to kill its performance (thank Intel’s chipset folks for that). You’d almost assuredly need an X58- or 890FX-based desktop platform, or something based on 5520 in the workstation space. Then again, if you’re in the market for a drive like this, “going cheap” probably wasn’t in the cards anyway.

The Future Of IBIS

In discussing IBIS, OCZ’s Ryan Petersen gave away some of the company’s plans for the drive’s future (it does seem to have a roadmap—it’s not a one-off product). While the architecture being used today is capable of up to 120,000 IOPS, OCZ expects to release a version in three months capable of twice that. From there, this first-gen HSDL implementation will be maxed out, and the interface speed will have to increase. Once they’re there, today’s hardware is going to get pushed down-market (a la Nvidia’s G92, for example), and a new generation will be launched up top.

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