[Beowulf] SSD prices

Michael Brown spambox at emboss.co.nz
Thu Dec 11 19:56:13 EST 2008


Greg Lindahl wrote:
>I was recently surprised to learn that SSD prices are down in the
> $2-$3 per gbyte range. I did a survey of one brand (OCZ) at NexTag
> and it was:
>
> 256 gigs = $700
> 128 gigs =  300
> 64 gigs =  180
> 32 gigs =   70

Alas, these drives have lousy random write performance. As in 4 IOps lousy. 
Read speed is pretty good, but since it appears to take 250 ms for an erase 
+ write cycle on the flash (during which other reads are blocked as well), 
it's got really rather limited usefulness. People have reported that Vista 
won't install on the drives, due to timeouts. This is also why the prices 
are so low - they're basically dumping them to get rid of them. Note that 
OCZ aren't alone in this issue - all of the "low cost" SSDs have the same 
issue since they're all just rebadges of the same OEM drive.

For good performance, you're AFAIK limited to the Intel X25's and similar. 
The 80 GB X25-M hits you for $528 according to NexTag, other good 64 GB SSDs 
are around the $450 - $500 mark, depending on the drive (I can't get NexTag 
to list them, it only shows a very high price for the MTRON 64 GB drive). 
They're still not a whole lot faster than spinning rust once you start to 
have some randomness in your writing. Reliability should be fine in laptops, 
though I'd be less keen to deploy a rack full of them - they're a lot more 
sensitive to electrical noise than traditional HDDs when both reading and 
writing, so their reliability in these situations depends on how good the 
ADC and DAC converters are in the chips, and how much space they burn for 
ECC. The fact that the manufacturers don't spec the uncorrected/miscorrected 
error rate under any circumstances makes me a tad worried. Also, the 
lifespan question is still unanswered - any particular page of MLC flash is 
still limited to about 10000 writes, so you've got to hope that your 
workload doesn't tickle the wear levelling algorithm the wrong way.


Cheers,
Michael 

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