Message-ID: <51958930.1010103@catalyst.net.nz>
Date: Fri, 17 May 2013 13:34:40 +1200
From: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
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To: climbingrose@gmail.com
CC: Tomas Vondra <tv@fuzzy.cz>, pgsql-performance@postgresql.org
Subject: Re: Reliability with RAID 10 SSD and Streaming Replication
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On 17/05/13 12:06, Tomas Vondra wrote:
> Hi,
>
> On 16.5.2013 16:46, Cuong Hoang wrote:

>> Pro for the master server. I'm aware of write cache issue on SSDs in
>> case of power loss. However, our hosting provider doesn't offer any
>> other choices of SSD drives with supercapacitor. To minimise risk, we
>> will also set up another RAID 10 SAS in streaming replication mode. For
>> our application, a few seconds of data loss is acceptable.
>
> Streaming replication allows zero data loss if used in synchronous mode.
>

I'm not sure synchronous replication is really an option here as it will 
slow the master down to spinning disk io speeds, unless the standby is 
configured with SSDs as well - which probably defeats the purpose of 
this setup.

On the other hand, if the system is so loaded that a pure SAS (spinning 
drive) solution can't keen up, then the standby lag may get to be way 
more than a few seconds...which means look out for huge data loss.

I'd be inclined to apply more leverage to hosting provider to source 
SSDs suitable for your needs, or change hosting providers.

Regards

Mark


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