Subject: Re: Postgres on NAS/NFS
From: "Joshua D. Drake" <jd@commandprompt.com>
Reply-To: jd@commandprompt.com
To: Greg Smith <greg@2ndquadrant.com>
Cc: Bryan Keller <bryanck@gmail.com>, pgsql-admin@postgresql.org
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Organization: Command Prompt, Inc.
Date: Wed, 16 Feb 2011 13:12:39 -0800
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On Wed, 2011-02-16 at 15:56 -0500, Greg Smith wrote:
> 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.

In short, use DAS or a SAN. iSCSI suffers from all kinds of performance
issues and NFS is just Michael Myers scary.

With DAS systems able to handle up 192 drives over 6Gb/s a second these
days, combined with a volume manager you can solve a lot of problems
without breaking the bank.

JD

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