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Re: Amazon EC2 | Any recent developments

From: Greg Smith <gsmith(at)gregsmith(dot)com>
To: Just Someone <just(dot)some(at)gmail(dot)com>
Cc: David Kerr <dmk(at)mr-paradox(dot)net>, pgsql-general(at)postgresql(dot)org
Subject: Re: Amazon EC2 | Any recent developments
Date: 2009-06-16 18:05:33
Message-ID: alpine.GSO.2.01.0906161357310.1266@westnet.com (view raw or flat)
Thread:
Lists: pgsql-general
On Tue, 16 Jun 2009, Just Someone wrote:

> In case the volume got corrupted (a very rare situation, as the EBS
> volumes are very durable), there are snapshots I can recover from and
> the WAL files I stream to another storage system (Amazon's S3).

I wouldn't go so far as to say "very durable", because the failure rate 
they aim for isn't really very high relative to what people expect when 
you use that term in a database context.  The most definitive commentary 
I've found on this is at 
http://solutions.amazonwebservices.com/connect/thread.jspa;jsessionid=96A862FA1DC393FCDD94DAF0B43CF4E7?messageID=111953 
where they say "we aim to provide an annual failure rate (AFR) of 0.1% - 
0.5% for volumes"; frankly, that's garbage to most database people.  But, 
as you say, when combined with an alternative backup strategy when that 
happens, the easy provisioning and such can give a reasonable system 
design for some goals.  You just have to recognize that the volumes are 
statistically pretty fragile compared to a traditional RAID configuration 
on dedicated hardware and plan accordingly.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD

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