Re: SSDs with Postgresql?

On Fri, Apr 29, 2011 at 1:23 AM, Toby Corkindale
<toby(dot)corkindale(at)strategicdata(dot)com(dot)au> wrote:
> On 29/04/11 16:35, Greg Smith wrote:
>>
>> On 04/26/2011 10:30 AM, Toby Corkindale wrote:
>>>
>>> I see Intel is/was claiming their SLC SSDs had a *minimum* lifetime of
>>> 2PB in writes for their 64GB disks; for your customer with a 50GB db
>>> and 20GB/day of WAL, that would work out at a minimum lifetime of a
>>> million days, or about 273 years!
>>> The cheaper "consumer grade" MLC drives should still last minimum 5
>>> years at 20GB/day according to their literature. (And what I found was
>>> fairly out of date)
>>> That doesn't seem too bad to me - I don't think I've worked anywhere
>>> that keeps their traditional spinning disks in service beyond 5 years
>>> either.
>>
>>
>> The comment I made there was that the 20GB/day system was a very small
>> customer. One busy server, who are also the ones most likely to want
>> SSD, I just watched recently chug through 16MB of WAL every 3
>> seconds=450GB/day. Now, you're right that those systems also aren't
>> running with a tiny amount of flash, either. But the write volume scales
>> along with the size, too. If you're heavily updating records in
>> particular, the WAL volume can be huge relative to the drive space
>> needed to store the result.
>
> For that sort of workload, it does sound like SSD isn't ideal.
> Although if the Intel figure of 2PB is to be believed, it'd still take >200
> years to wear the drives out (assuming you'll need at least ten 64 GB disks
> just to store the DB on).
> (Reference: http://download.intel.com/design/flash/nand/extreme/319984.pdf )

I think you misunderstood. He's not storing 480GB on the drives,
that's how much WAL is moving across it. It could easily be a single
80GB SSD drive or something like that.