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SSD and RAID

From: Mark Kirkwood <mark(dot)kirkwood(at)catalyst(dot)net(dot)nz>
To: pgsql-performance(at)postgresql(dot)org
Subject: SSD and RAID
Date: 2012-03-05 22:37:25
Message-ID: 4F554025.9040101@catalyst.net.nz (view raw or flat)
Thread:
Lists: pgsql-performance
Where I work we are starting to look at using SSDs for database server 
storage. Despite the higher per unit cost it is quite attractive to 
replace 6-8 SAS drives in RAID 10 by a pair of SSD in RAID 1 that will 
probably perform better and use less power.

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.

One option to get around the simultaneous firmware failure is to be to 
get 2 *similar* drives from different manufactures (e.g OCZ Vertex 32 
and Intel 520 - both Sandforce but different firmware setup). However 
using different manufacturers drives is a pest (e.g different smart 
codes maintained and/or different meanings for the same codes)

What are other folks who are using SSDs doing?

Cheers

Mark

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Subject: Re: SSD and RAID
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Subject: Re: Advice sought : new database server

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