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Re: the RAID question, again

From: Vincent van Leeuwen <pgsql(dot)spam(at)vinz(dot)nl>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: the RAID question, again
Date: 2003-04-22 12:11:50
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Lists: pgsql-performance
On 2003-04-16 19:32:54 -0700, Nikolaus Dilger wrote:
> One improvement area may be to put all 6 disks into a
> RAID 10 group.  That way you have more I/O bandwith. 

A concern I have about that setup is that a large WAL write will have to wait
for 6 spindles to write the data before returning instead of 2 spindles. But
as you say it does create way more I/O bandwidth. I think I'll just test that
when the box is here instead of speculating further :)

> 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.

On 2003-04-16 20:20:50 -0700, Josh Berkus wrote:
> Nickolaus has a good point.   With a high-end Linux server, and a medium-end
> RAID card, it's sometimes faster to use Linux software RAID than harware
> raid.  Not all the time, though.

I've heard rumors that software raid performs poor when stacking raid layers
(raid 0 on raid 1). Not sure if that's still true though. My own experiences
with linux software raid (raid 5 on a low-cost fileserver for personal use)
are very good (especially in the reliability department, I've recovered from
two-disk failures due to controllers hanging up with only a few percent data
loss), although I've never been overly concerned with performance on that
setup so haven't really tested that.

But if this controller is medium-end, could anyone recommend a high-end RAID
card that has excellent linux support? One of the things I especially like
about ICP Vortex products is the official linux support and the excellent
software utility for monitoring and (re)configuring the raid arrays. Comes in
handy when replacing hot-spares and rebuilding failed arrays while keeping
the box running :)

Vincent van Leeuwen
Media Design -

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