On Tue, Dec 11, 2012 at 10:48 AM, Bruce Momjian <bruce@momjian.us> wrote:
> On Mon, Dec 10, 2012 at 02:05:09AM -0500, Greg Smith wrote:
>> On 11/14/12 2:11 AM, Toby Corkindale wrote:
>> >So on the face of it, I think the Sandforce-based drives are probably a
>> >winner here, so I should look at the Intel 520s for evaluation, and
>> >whatever the enterprise equivalent are for production.
>>
>> As far as I know the 520 series drives fail the requirements
>> outlined at http://wiki.postgresql.org/wiki/Reliable_Writes and you
>> can expect occasional data corruption after a crash when using them.
>> As such, any performance results you get back are fake. You can't
>> trust the same results will come back from their drives that do
>> handle writes correctly. I'm not aware of any SSD with one of these
>> compressing Sandforce controller that's on the market right now that
>> does this correctly; they're all broken for database use. The quick
>> rule of thumb is that if the manufacturer doesn't brag about the
>> capacitors on the drive, it doesn't have any and isn't reliable for
>> PostgreSQL.
>>
>> The safe Intel SSD models state very clearly in the specifications
>> how they write data in case of a crash. The data sheet for the 320
>> series drives for example says "To reduce potential data loss, the
>> Intel® SSD 320 Series also detects and protects from unexpected
>> system power loss by saving all cached data in the process of being
>> written before shutting down". The other model I've deployed and
>> know is safe are the 710 series models, which are the same basic
>> drive but with different quality flash and tuning for longevity.
>> See http://blog.2ndquadrant.com/intel_ssds_lifetime_and_the_32/ for
>> details. The 710 series drives are quite a bit more expensive than
>> Intel's other models.
>
> It looks like the newer Intel 330 SSD also lacks a capacitor.
I believe that's the case. The only choices today are the 320, 710,
and the upcoming DC S3700 (which looks explicitly designed for
database use).
merlin
