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You're still concentrating on consumer level drives. The stec drives
emc is using for instance, exhibit none of the behaviors you describe.
While I agree from a cost perspective, fusionIO's product is more
attractice, you blanket statements on flash are inaccurate.
On 5/27/08, Bob Friesenhahn <bfriesen@xxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, 26 May 2008, Mertol Ozyoney wrote:
>
>> It's true that NAND based falsh's wear out under heavy load. Regular
>> consumer grade nand drives will wear out the extra cells pretty rapidly.
>> (in
>> a year or so) However enterprise grade SSD disks are fine tuned to with
>> stand continous writes for more than 10 years
>
> It is incorrect to classify wear in terms of years without also
> specifying update behavior. NAND FLASH sectors can withstand 100,000
> to (sometimes) 1,000,000 write-erase-cycles. In normal filesystem
> use, there are far more reads than writes and the size of the storage
> device is much larger than the the data re-written. Even in server
> use, only a small fraction of the data is updated. A device used to
> cache writes will be written to as often as it is read from (or
> perhaps more often). If the cache device storage is fully occupied,
> then wear leveling algorithms based on statistics do not have much
> opportunity to work.
>
> If the underlying device sectors are good for 100,000
> write-erase-cycles and the entire device is re-written once per
> second, then the device is not going to last very long (27 hours).
> Of course the write performance for these devices is quite poor
> (8-120MB/second) and the write performace seems to be proportional to
> the total storage size so it is quite unlikely that you could re-write
> a suitably performant device once per second. The performance of
> FLASH SSDs does not seem very appropriate for use as a write cache
> device.
>
> There is a useful guide to these devices at
> "http://www.storagesearch.com/ssd-buyers-guide.html";.
>
> SRAM-based cache devices which plug into a PCI-X or PCI-Express slot
> seem far more appropriate for use as a write cache than a slow SATA
> device. At least 5X or 10X the performance is available by this
> means.
>
> Bob
> ======================================
> Bob Friesenhahn
> bfriesen@xxxxxxxxxxxxxxxxxxx, http://www.simplesystems.org/users/bfriesen/
> GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
>
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