From: | Greg Smith <greg(at)2ndquadrant(dot)com> |
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To: | Jesper Krogh <jesper(at)krogh(dot)cc> |
Cc: | Balkrishna Sharma <b_ki(at)hotmail(dot)com>, scott(dot)marlowe(at)gmail(dot)com, pgsql-admin(at)postgresql(dot)org |
Subject: | Re: Asynchronous commit | Transaction loss at server crash |
Date: | 2010-05-20 22:04:22 |
Message-ID: | 4BF5B1E6.1020701@2ndquadrant.com |
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Lists: | pgsql-admin |
Jesper Krogh wrote:
> A Battery Backed raid controller is not that expensive. (in the range
> of 1 or 2 SSD disks).
> And it is (more or less) a silverbullet to the task you describe.
Maybe even less; in order to get a SSD that's reliable at all in terms
of good crash recovery, you have buy a fairly expensive one. Also, and
this is really important, you really don't want to deploy onto a single
SSD and put critical system files there. Their failure rates are not
that low. You need to put them into a RAID-1 setup and budget for two
of them, which brings you right back to
Also, it's questionable whether a SSD is even going to be faster than
standard disks for the sequential WAL writes anyway, once a non-volatile
write cache is available. Sequential writes to SSD are the area where
the gap in performance between them and spinning disks is the smallest.
> Plugging your system (SSD's) with an UPS and trusting it fully
> could solve most of the problems (running in writeback mode).
UPS batteries fail, and people accidentally knock out over server power
cords. It's a pretty bad server that can't survive someone tripping
over the cord while it's busy, and that's the situation the "use a UPS"
idea doesn't improve.
--
Greg Smith 2ndQuadrant US Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com www.2ndQuadrant.us
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