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Re: Anyone using a SAN?

From: "Scott Marlowe" <scott(dot)marlowe(at)gmail(dot)com>
To: "Greg Smith" <gsmith(at)gregsmith(dot)com>
Cc: "Tobias Brox" <tobias(at)nordicbet(dot)com>, "Peter Koczan" <pjkoczan(at)gmail(dot)com>, pgsql-performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Anyone using a SAN?
Date: 2008-02-14 00:55:49
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
On Feb 13, 2008 5:02 PM, Greg Smith <gsmith(at)gregsmith(dot)com> wrote:
> On Wed, 13 Feb 2008, Tobias Brox wrote:
> > What I'm told is that the state-of-the-art SAN allows for an "insane
> > amount" of hard disks to be installed, much more than what would fit
> > into any decent database server.
> You can attach a surpringly large number of drives to a server nowadays,
> but in general it's easier to manage larger numbers of them on a SAN.
> Also, there are significant redundancy improvements using a SAN that are
> worth quite a bit in some enterprise environments.  Being able to connect
> all the drives, no matter how many, to two or more machines at once
> trivially is typically easier to setup on a SAN than when you're using
> more direct storage.


> There's no universal advantage on either side here, just a different set
> of trade-offs.  Certainly you'll never come close to the performance/$
> direct storage gets you if you buy that in SAN form instead, but at higher
> budgets or feature requirements they may make sense anyway.

I agree with everything you've said here, and you've said it far more
clearly than I could have.

I'd like to add that it may still be feasable to have a SAN and a db
with locally attached storage.  Talk the boss into a 4 port caching
SAS controller and four very fast hard drives or something else on the
server so that you can run tests to compare the performance of a
rather limited on board RAID set to the big SAN.  For certain kinds of
things, like loading tables, it will still be a very good idea to have
local drives for caching and transforming data and such.

Going further, the argument for putting the db onto the SAN may be
weakened if the amount of data on the db server can't and likely won't
require a lot of space.  A lot of backend office dbs are running in
the sub gigabyte range and will never grow to the size of the social
security database.  Even with dozens of apps, an in house db server
might be using no more than a few dozen gigabytes of storage.  Given
the cost and performance of large SAS and SATA drives, it's not all
unlikely that you can fit everything you need for the next five years
on a single set of disks on a server that's twice as powerful as most
internal db servers need.

You can hide the cost of the extra drives in the shadow of the receipt
for the SAN.

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