Message-ID: <4DC0D968.3030106@krogh.cc>
Date: Wed, 04 May 2011 06:43:20 +0200
From: Jesper Krogh <jesper@krogh.cc>
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To: Willy-Bas Loos <willybas@gmail.com>
CC: pgsql-performance@postgresql.org
Subject: Re: [PERFORMANCE] expanding to SAN: which portion best
 to move
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On 2011-05-03 17:52, Willy-Bas Loos wrote:
> Our database has gotten rather large and we are running out of disk space.
> our disks are 15K rpm SAS disks in RAID 10.
>
> We are going to rent some space on a FibreChannel SAN.
> That gives us the opportunity to separate the data and the indexes.
> Now i thought it would be best to move the indexes to the SAN and leave the
> data on the disks, since the disks are better at sequential I/O and the SAN
> will have lots of random I/O since there are lots of users on it.
>
> Is that a wise thing to do?

If you're satisfied with the current performance then it should be safe
to keep the indices and move the data, the risk of the SAN performing
worse on sequential I/O is not that high. But without testing and
knowledge about the SAN then it is hard to say if what you currently
have is better or worse than the SAN. The vendor may have a "way better 
san",
but is may also be shared among 200 other hosts connected over iSCSI or FC
so your share may be even worse than what you currently have.

Without insight and testing is it hard to guess. I've pretty much come
to the conclusion of going the DAS way every time, but it all depends on
what your end looks like.

-- 
Jesper