Bye-bye hard drive, hello flash

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Hybrid Drives

Actually, the hybrid drives I'm familiar with don't use flash RAM at all, but rather just standard DRAM. (I admit however it's been a few years since I've dealt with them.) They contain enough RAM to cache the entire disk (which actually limits the disk size). As soon as they receive power, they dump the entire disk to RAM, all the while charging up an extended capacity capacitor or rechargeable battery. Once loaded, the drive becomes active, all the I/O calls being sent to and from RAM only, leaving the physical drive alone.

It operates this way until the power is cut, at which time it runs on the capacitor/battery, uses its charge to keep the drive spinning and dump the entire RAM contents to the physical disk. Once done, the drive stays alive until power runs out so that if the computer is restarted in the mean time, the drive will be ready to go and run in a near instant-on state.

The advantages are speed, longevity, and when compared to SSD alternatives, cost.

Disadvantages are power consumption (the ones I've dealt with did not spin down) since they power both the physical HDD and the DRAM, and the difficult in defect testing; the RAM functions are transparent to the OS, making the platters invisible. IOW, doing a scandisk will actually scan the RAM, not the physical platters. Therefore, they can't be tested with standard tools. This may not be a large concern, since the lack of physical write cycles greatly increases the drive's lifespan, however this same problem also means that multi-pass secure erase tools (eg DoD erase) are useless, since no writing will physically take place until the system is shut down, in which only a single pass dump will be performed.

With a few power saving tweaks, yes they may be a viable alternative in notebooks for those speed minded, but you have to keep in mind that the RAM is still expensive; these drives are far more expensive than standard HDDs for all the extra parts involved.

Posted by: D-cat   Posted on: 01/04/06 You are currently: a Guest | Members login | Terms of Use

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