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Re: Postgres on NAS/NFS

From: Greg Smith <greg(at)2ndquadrant(dot)com>
To: Bryan Keller <bryanck(at)gmail(dot)com>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: Postgres on NAS/NFS
Date: 2011-02-16 20:56:13
Message-ID: 4D5C39ED.9040609@2ndquadrant.com (view raw or flat)
Thread:
Lists: pgsql-admin
Bryan Keller wrote:
> It sounds like NFS is a viable solution nowadays. I a still going to shoot for using iSCSI, given it is a block-level protocol rather than file-level, it seems to me it would be better suited to database I/O.
>   

Please digest carefully where Joe Conway pointed out that it took them 
major kernel-level work to get NFS working reliably on Linux.  On 
anything but Solaris, I consider NFS a major risk still; nothing has 
improved "nowadays" relative to when people used to report regular 
database corruption running it on other operating systems.  Make sure 
you read 
http://www.time-travellers.org/shane/papers/NFS_considered_harmful.html 
and mull over the warnings in there before you assume it will work, too.

I don't think I've ever heard from someone happy with an iSCSI 
deployment, either.  The only way you could make an NFS+iSCSI storage 
solution worse is to also use RAID5 on the NAS.

I'd suggest taking a look at 
http://wiki.postgresql.org/wiki/Shared_Storage and consider how you're 
going to handle fencing issues as well here.  One of the reasons SANs 
tend to be preferred in this area is because fencing at the 
fiber-channel switch level is pretty straightforward.  DAS running over 
fiber-channel can offer the same basic features though, it's just not as 
common to use a switch in that environment.

-- 
Greg Smith   2ndQuadrant US    greg(at)2ndQuadrant(dot)com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us
"PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books


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