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Date:      Wed, 29 Aug 2007 20:43:07 +0200
From:      Kirill Ponomarew <krion@voodoo.bawue.com>
To:        Vivek Khera <vivek@khera.org>
Cc:        FreeBSD Stable <freebsd-stable@freebsd.org>
Subject:   Re: large RAID volume partition strategy
Message-ID:  <20070829184306.GC42906@voodoo.bawue.com>
In-Reply-To: <94ECF72B-B0E9-492C-8279-29989FAAE19C@khera.org>
References:  <31BB09D7-B58A-47AC-8DD1-6BB8141170D8@khera.org> <fa5b4v$8e5$1@sea.gmane.org> <EED39309-A95F-4A2D-8E35-C1650A55E482@khera.org> <fa5men$v5r$1@sea.gmane.org> <94ECF72B-B0E9-492C-8279-29989FAAE19C@khera.org>

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On Wed, Aug 29, 2007 at 10:07:19AM -0400, Vivek Khera wrote:
> 
> On Aug 17, 2007, at 10:44 PM, Ivan Voras wrote:
> 
>> 
>> fdisk and bsdlabels both have a limit: because of the way they store the
>> data about the disk space they span, they can't store values that
>> reference space > 2 TB. In particular, every partition must start at an
>> offset <= 2 TB, and cannot be larger than 2 TB.
> 
> Thanks.  This is good advice (along with your other note about doing it in 
> the RAID volume manager).  Nearly everyone else decided to jump on the raid 
> level instead and spew forth the "RAID10 is better for database" party 
> line.  Well to you folks: once you have 1Gb cache and a lot of disks, there 
> is not much difference between RAID10 and RAID5 or RAID6 in my testing.
 
What type I/O did you test, random read/writes, sequential writes ?
The performance of RAID group always depends on what software you
run on your RAID group.  If it's database, be prepared for many
random read/writes, hence dd(1) tests would be useless.

> I ended up making 6 RAID volumes across all the disks to maximize spindle 
> counts and strip the data at 16kB.  This seems to work well, and I can 
> assign the other partition as I need later on.
> 
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-Kirill



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