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Seagate brewing bizarre Flash/Platter chimera

Interweb mutterings of unholy experiments

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A Greek website is reporting that a combined solid state and spinning disk drive may be on the way from Seagate.

The hw box story says the hybrid Momentus XT will combine a 4GB solid state drive (SSD) with a 7200rpm rotating hard disk offering 250, 320 or 500GB of capacity.

There will be a 32MB cache, a 3Gbit/s SATA interface, and native command queuing (NCQ). The article mentions an 80 per cent performance improvement over a 7200rpm hard drive on a PCMark Vantage test.

Targeted devices for the flash-using Momentus XT are notebooks, workstations and small form-factor desktop PCs.

It sounds exciting; but if it is real, this thing has a hard drive, a 32MB cache and a 4GB SSD, and is evidently not a cache - or at least not the front-end cache as the 32MB of RAM does that job. So what is it? SSDs are good for much faster read and write I/O than hard drives, but what data goes onto the SSD and how does it get there?

Incoming write data could go straight into the SSD and so complete, from the host's point of view, more quickly. The firmware could then write it to the hard drive in the background.

How would a read request be dealt with? Is it farmed out to the SSD and the hard drive simultaneously with the first to answer handling the request? Or does it go the SSD first and, if that says no, on to the hard drive? There's lots of uncertainty here, as is the way with rumours, and this hybrid drive may be a figment of someone's imagination.

Previous attempts by HDD suppliers to add flash foundered with Windows Vista back in 2007. Toshiba recently said it was considering whether to build a hybrid SSD and HDD device itself.

Seagate responded to an enquiry by saying it does not comment on rumour or speculation about its intentions. ®

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