Date: Fri, 4 Aug 2017 11:54:08 +0200
From: "Jehan-Guillaume (ioguix) de Rorthais" <ioguix@free.fr>
To: Purav Chovatia <puravc@gmail.com>
Cc: pgsql-admin@postgresql.org
Subject: Re: Postgres HA using Shared Disk Solution
Message-ID: <20170804115408.5962105b@firost>
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On Fri, 4 Aug 2017 13:30:24 +0530
Purav Chovatia <puravc@gmail.com> wrote:

> Hello All,
> 
> I have been researching for possible HA solutions for postgres. I find
> shared disk solution (either using Linux-HA or RHCS) to be a very good
> solution. Especially for us, because our databases are big and they do a
> lot of IO so we deploy a lot of disks.
> 
> However, research on the internet shows that a shared disk solution is not
> very commonly deployed when it comes to postgres. People mostly go for
> Streaming Replication/Warm/Hot-Standby which to me are more like DR
> solutions.
> 
> Is my research correct or that is not so? for e.g. this was the only post
> that I came across, and that too as old as 2012:
> https://www.postgresql.org/message-id/4F68E989.7080101%40d2.com
> 
> Given our IO requirement, if we go for Streaming Replication instead, then
> our storage needs double and that increases the cost.
> 
> Can someone confirm, if shared disk clustering is fairly common or no in
> the postgres world? If no, why is it so - can somebody enlighten me pls.

Shared disk is totally fine. It just requires a warm node useless for
day-to-day usage compare to HA on a streaming replication architecture where
the standby can be involved as a RO node.

Just make sure that:
* your SAN does not allow more than one server at a time to access the data
* you are able to fence the other node or its access to the disk
* extensive failover scenarios has been tested
* all required documentation has been written on your side to manage the cluster

As a bonus, make sure to use Pacemaker, with a recent distro (RHEL 7, CentOS 7,
Debian 9).

Regards,
-- 
Jehan-Guillaume de Rorthais
Dalibo


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