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Re: 3ware trivia overload

From: David Rees <drees76(at)gmail(dot)com>
To: George Sexton <georges(at)mhsoftware(dot)com>
Cc: Greg Smith <greg(at)2ndquadrant(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: 3ware trivia overload
Date: 2010-09-20 22:09:41
Message-ID: AANLkTinX5Aeu_2O+PG2j8wrGecSf1rJV0HXvrxR+_5f7@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Mon, Sep 20, 2010 at 2:54 PM, George Sexton <georges(at)mhsoftware(dot)com> wrote:
> I'll throw in my 2 cents worth:
>
> 1) Performance using RAID 1 for reads sucks. You would expect throughput to
> double in this configuration, but it doesn't. That said, performance for
> RAID 1 is not noticeably worse than Linux MD. My testing showed the 3Ware
> controller to be about 20% faster than Linux MD for RAID 1.

No performance improvement is expected for streaming reads in any
non-striped RAID1.  Random reads should nearly double in throughput.

You can use Linux's software RAID10 module to improve streaming reads
of a "mirror" using the "far" layout which in effect stripes the data
across 2 disks at the expense of some hit in streaming write
performance.  Testing is required to determine if this tradeoff works
for your workload or not.

-Dave

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