|From:||Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>|
|To:||Greg Smith <greg(at)2ndquadrant(dot)com>|
|Cc:||"Henry C(dot)" <henka(at)cityweb(dot)co(dot)za>, Leonardo Francalanci <m_lists(at)yahoo(dot)it>, pgsql-general(at)postgresql(dot)org|
|Subject:||Re: SSDs with Postgresql?|
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On Thu, Apr 14, 2011 at 1:14 PM, Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
> And the idea that a UPS is sufficient to protect against that even happening in
> wildly optimistic.
Note that the real danger in relying on a UPS is that most power
conditioning / UPS setups tend to fail in total, not in parts. The
two times I've seen it happen, the whole grid shut down completely for
a few hours. The first time we had Oracle, Ingress, Sybase,
SQL-Server, etc. etc. database server across the company corrupted.
DAYS of recovery time, and since they all failed at once, the machines
in replication got corrupted as well. Restoring production dbs from
backups took days.
The only machine to survive was the corporate intranet running pgsql
on twin 15k SCSI drives with a proven reliable battery backed
controller on it. It was mine. This was a company that lost
something like $10k a minute for downtime. And the downtime was
measured not in seconds, minutes or hours, but days because everyone
had said the same thing, "The UPS and power conditioners make power
plug pull survivability a non issue." When the only machine with an
uncorrupted database is the corporate intranet server the 24/7
production guys look pretty stupid. They also suddenly decided to
start doing power plug pull tests on all database servers.
To make matters worse, the kind of system to NEED the higher
throughput from SSDs is likely the kind of system to be the worst kind
to suffer downtime due to corruption. OTOH, restores from backups
should run pretty fast. :)
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