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Re: the RAID question, again

From: "Nikolaus Dilger" <nikolaus(at)dilger(dot)cc>
To: pgsql(dot)spam(at)vinz(dot)nl
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: the RAID question, again
Date: 2003-04-17 02:32:54
Message-ID: 20030416193256.25788.h006.c001.wm@mail.dilger.cc.criticalpath.net (view raw or flat)
Thread:
Lists: pgsql-performance
Vincent,

In my eyes the best disk I/O configuration is a balance
of performance, price and administrative effort.

Your set-up looks relatively good.  Howver, price seems
not to be your greatest concern.  Otherwise you would
favor RAID 5 and/or leave out the spare disk.

One improvement area may be to put all 6 disks into a
RAID 10 group.  That way you have more I/O bandwith. 

One watchout is that the main memory of your machine
may be better than the one of your RAID controller.
The RAID controller has Integrated 128MB PC133 ECC
SDRAM.  You did not state what kind of memory your
server has.

Regards,
Nikolaus

On Wed, 16 Apr 2003 18:26:58 +0200, Vincent van Leeuwen
wrote:

> 
> Hi,
> 
> I want to ask the 'which RAID setup is best for
> PostgreSQL?' question again.
> I've read a large portion of the archives of this
list,
> but generally the
> answer is 'depends on your needs' with a few different
> camps.
> 
> My needs are as follows: dedicated PostgreSQL server
> for a website, which does
> much more select queries than insert/updates
(although,
> due to a lot of
> caching outside the database, we will be doing more
> updates than usual for a
> website).
> 
> The machine which will be built for this is going to
be
> something like a dual
> Xeon 2.4GHz, 4GB RAM, and a SCSI hardware RAID
> controller with some cache RAM
> and 6-7 36GB 15K rpm disks. We have good experiences
> with ICP Vortex
> controllers, so I'll probably end up buying on of
those
> again (the GDT8514RZ
> looks nice:
>
http://www.icp-vortex.com/english/product/pci/rzu320/8514rz_e.htm
> )
> 
> We normally use Debian linux with a 2.4 kernel, but
> we're thinking we might
> play around with FreeBSD and see how that runs before
> making the final choice.
> 
> The RAID setup I have in my head is as follows:
> 
> 4 disks for a RAID 10 array, for the PG data area
> 2 disks for a RAID 1 array, for the OS, swap (it won't
> swap) and, most
> importantly, WAL files
> 1 disk for hot spare
> 
> RAID 1 isn't ideal for a WAL disks because of the
> (small) write penalty, but
> I'm not sure I want to risk losing the WAL files. As
> far as I know PG doesn't
> really like losing them :) This array shouldn't see
> much I/O outside of the
> WAL files, since the OS and PG itself should be
> completely in RAM when it's
> started up.
> 
> RAID 5 is more cost-effective for the data storage,
but
> write-performance is
> much lower than RAID 10.
> 
> The hot-spare is non-negotiable, it has saved my life
a
> number of times ;)
> 
> Performance and reliability are the prime concerns for
> this setup. We normally
> run our boxes at extremely high loads because we don't
> have the budget we
> need. Cost is an issue, but since our website is
always
> growing at an insane
> pace I'd rather drop some cash on a fast server now
and
> hope to hold out till
> the end of this year than having to rush out and buy
> another mediocre server
> in a few months.
> 
> Am I on the right track or does anyone have any tips I
> could use?
> 
> 
> On a side note: this box will be bought a few days or
> weeks from now and
> tested during a week or so before we put it in our
> production environment (if
> everything goes well). If anyone is interested in any
> benchmark results from
> it (possibly even FreeBSD vs Linux :)) that can
> probably be arranged.
> 
> 
> Vincent van Leeuwen
> Media Design - http://www.mediadesign.nl/
> 
> 
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