DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma;
	h=subject:mime-version:content-type:from:in-reply-to:date:cc
	:content-transfer-encoding:message-id:references:to:x-mailer;
	b=GcD7DakAQ9406Rya2O7bKuDHZWb4cu9CRRlqIiAIHnrEjyMauQ4kpJrpW1PEQcnfUI
	fCTJ/EKwC4xsFklwMZRQNtojjuK65NuIHM2fCsTkoYf2a+x244chNZFSMFscmFjIMh0t
	ly32nSEPPuoH6ArEzh2Kt9H5mVXkF4794qz18=
Subject: Re: Performance advice for a new low(er)-power server
Mime-Version: 1.0 (Apple Message framework v1084)
Content-Type: text/plain; charset=us-ascii
From: Haestan <haestan@gmail.com>
In-Reply-To: <4DFA4EB7.1020701@2ndQuadrant.com>
Date: Fri, 17 Jun 2011 11:13:32 +0200
Cc: pgsql-performance@postgresql.org
Content-Transfer-Encoding: quoted-printable
Message-Id: <EEC749F3-1859-4FC7-8CA4-81404003EE45@gmail.com>
References: <BANLkTinXa4ZVigTQ7Q=05saam_3GZdyx7g@mail.gmail.com>
	<4DFA4EB7.1020701@2ndQuadrant.com>
To: Greg Smith <greg@2ndQuadrant.com>


On Jun 16, 2011, at 20:43, Greg Smith wrote:
> The layout you proposed (OS+WAL , data) might be effective, but if =
your write volume is low it may not be much of an improvement at all =
over a simple RAID1 of two drives.  The odds that you are going to =
correctly lay out individual sections of a disk array with only two =
pairs to spread the data across aren't good.  If this is all you have to =
work with, a 4-disk RAID10 would at least guarantee you're taking =
advantage of all four drives.  With that controller, it should be almost =
twice as fast in all cases as hooking up only two drives.

The data is more or less constantly rewritten (it contains hourly =
updated travel related data). Therefore, I really tend to buy 4 disks =
from the start on.

> There is another possibility I would suggest you consider.  You could =
buy the server with a single pair of drives now, then wait to see what =
performance is like before filling the other two slots.  It is far =
easier to figure out what drive technology makes sense if you have =
measurements from an existing system to guide that decision.  And you =
may be able to get newer drives from your vendor that slide into the =
empty slots.  You may not ever even need more than a single RAID-1 pair. =
 I see lots of people waste money on drives that would be better spent =
on RAM.

Actually, there are already two older servers in place right now. The =
data is about 14GB in size and slowly rising. Considering the price for =
RAM I can easily afford to install more RAM than the db data is in size. =
I was aiming for 24GB. But even then, I cannot be sure that no queries =
will read from the disk. AFAIK, there is no way to force all the data to =
stay in cache (shared_buffers for example).=20

Thank you for your input so far.

Regards,

Tom.=