Date: Mon, 12 Aug 2013 16:05:04 -0400
From: Bruce Momjian <bruce@momjian.us>
To: "Joshua D. Drake" <jd@commandprompt.com>
Cc: "David F. Skoll" <dfs@roaringpenguin.com>, pgsql-admin@postgresql.org
Subject: Re: Opinions on SSDs
Message-ID: <20130812200504.GA12496@momjian.us>
References: <20130812112833.65a97285@hydrogen.roaringpenguin.com>
 <52090030.4000503@commandprompt.com>
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On Mon, Aug 12, 2013 at 08:33:04AM -0700, Joshua D. Drake wrote:
> >1) Has anyone had experience with Intel 520 SSDs?  Are they reliable?
> >When they fail, do they fail nicely (ie, failure detected and bad drive
> >removed from RAID array) or horribly (data silently corrupted...) ?
> 
> I don't recall if the 520s have powerloss protection but you will
> want to check that.

I am pretty sure they don't.  The only options are the Intel 320 and
710, I think.  Here is a blog about it:

	http://blog.2ndquadrant.com/intel_ssds_lifetime_and_the_32/

Look for "Enhanced Power Loss Data Protection".  Intel does not make it
easy to find all drive that have it --- you have to look at each spec
sheet.

> >2) Is this RAID arrangement sensible?  I've seen reports where some
> >people keep the pg_xlog directory on a separate RAID array, but I
> >don't really see the advantage with SSDs.
> 
> Put the pg_xlog on spindles, they are more than fast enough and
> won't eat up the write life of your SSDs.

Given its small size and need for fast fsync, I have WAL on SSDs, and
the data on magnetic disk.  You are right the WAL can generate a lot of
writes, but just use smartctl monitoring and replace the SSD when
needed.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +


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