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Re: SSD and RAID

From: Andrea Suisani <sickpig(at)opinioni(dot)net>
To: Yeb Havinga <yebhavinga(at)gmail(dot)com>
Cc: Mark Kirkwood <mark(dot)kirkwood(at)catalyst(dot)net(dot)nz>, pgsql-performance(at)postgresql(dot)org
Subject: Re: SSD and RAID
Date: 2012-03-06 08:34:15
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Lists: pgsql-performance
On 03/06/2012 09:17 AM, Yeb Havinga wrote:
> On 2012-03-05 23:37, Mark Kirkwood wrote:
>> Which brings up the question of should it be a pair in RAID 1 or just a singe drive? Traditionally this would have been a no brainer "Of course you want RAID 1 or RAID 10"! However our experience with SSD failure modes points to firmware bugs as primary source of trouble - and these are likely to
>> impact both drives (nearly) simultaneously in a RAID 1 configuration. Also the other major issue to watch - flash write limit exhaustion - is also likely to hit at the same time for a pair of drives in RAID 1.
>> What are other folks who are using SSDs doing?
> This is exactly the reason why in a set of new hardware I'm currently evaluating two different brands of manufacturers for the spindles (behind bbwc for wal, os, archives etc) and ssds (on mb sata ports). For the ssd's we've chosen the Intel 710 and OCZ Vertex 2 PRO, however that last one was EOL
> and OCZ offered to replace it by the Deneva 2 ( Still waiting for a test Deneva though.
> One thing to note is that linux software raid with md doesn't support discard, which might shorten the drive's expected lifetime. To get some numbers I tested the raid 1 of ssd's setup for mediawear under a PostgreSQL load earlier, see
> <Greg Smith imitation mode on>I would recommended that for every ssd considered for production use, test the ssd with on a filesystem that's mounted the same as you would with your data (e.g. with xfs or ext4 with nobarrier), and also do a mediawear test like the one described in the
> linked pgsql-general threar above, especially if you're chosing to run on non-enterprise marketed ssds.</>
> regards,
> Yeb
> PS: we applied the same philosophy (different brands) also to motherboards, io controllers and memory, but after testing, we liked one IO controllers software so much more than the other so we chose to have only one. Also stream memory performance of one motherboard showed a significant performance
> regression in the higher thread counts that we decided to go for the other brand for all servers.

care to share motherboard winning model?


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