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Re: Question on placing database on a network attached storage

From: Chris Travers <chris(at)travelamericas(dot)com>
To: N/A <srichardjanet(at)charter(dot)net>
Cc: Chris Travers <chris(at)verkiel(dot)metatrontech(dot)com>,pgsql-admin(at)postgresql(dot)org
Subject: Re: Question on placing database on a network attached storage
Date: 2005-07-30 21:59:30
Message-ID: 42EBF842.5090306@travelamericas.com (view raw or flat)
Thread:
Lists: pgsql-admin
N/A wrote:

>Chris,
>
>The NAS is a Network Appliance 920c.  I understand that an individual file
>while be "intact" during a snap, (not sure I believe it, but that's what I'm
>told).
>
Depending on the way that data is journalled, this may be a possibility 
(istr XFS is able to do this).

>  The NAS may be able to monitor the state of an individual file and
>not "snap" it if it is on an "open" state or has a pending write, or some
>such, but as the NAS has no knowledge of groups of files that need to exist
>in a known state, (it deals on the file level), it cannot guarantee a
>consistent state across a group of files.
>
That is a serious concern.  Every table in PostgreSQL consists of at 
least one physical file.  Transactions may touch several of these 
files.  While it is not impossible to solve this problem (as I 
mentioned, I think XFS has this capability), it is hardly trivial or 
something you would normally expect.

Also I wonder what the impact of several Postmasters trying to access 
data over NFS would be.

Best Wishes,
Chris Travers

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