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Re: Tablespaces on a raid configuration

From: Merlin Moncure <mmoncure(at)gmail(dot)com>
To: Andrew Dunstan <andrew(at)dunslane(dot)net>
Cc: "Campbell, Lance" <lance(at)illinois(dot)edu>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Tablespaces on a raid configuration
Date: 2012-03-30 16:11:40
Message-ID: CAHyXU0x6wC_0G4HzUzEZCuNaPXgmrsEyaxJf-VDLuKnNojyHYQ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Fri, Mar 30, 2012 at 10:02 AM, Andrew Dunstan <andrew(at)dunslane(dot)net> wrote:
> Not answering your question, but standard advice is not to use RAID 5 or 6,
> but RAID 10 for databases. Not sure if that still hold if you're using SSDs.

Yeah, for SSD the equations may change.  Parity based RAID has two
problems: performance due to writes having to do a read before writing
in order to calculate parity and safety (especially for raid 5) since
you are at greater risk of having a second drive pop while you're
rebuilding your volume.  In both things the SSD might significantly
reduce the negative impacts: read and write performance are highly
asymmetric greatly reducing or even eliminating observed cost of the
'write hole'.  Also, huge sequential speeds and generally smaller
device sizes mean very rapid rebuild time.   Also, higher cost/gb can
play in.  Food for thought.

merlin

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