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Re: A little RAID experiment

To: Stefan Ring <stefanrin@xxxxxxxxx>
Subject: Re: A little RAID experiment
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Wed, 30 May 2012 20:30:22 -0500
Cc: Linux fs XFS <xfs@xxxxxxxxxxx>
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On 5/30/2012 6:07 AM, Stefan Ring wrote:
> On Tue, May 1, 2012 at 12:46 PM, Stefan Ring <stefanrin@xxxxxxxxx> wrote:
>>> Stefan, you should be able to simply clear the P410i configuration in
>>> the BIOS, power down, then simply connect the 6 drive backplane cable to
>>> the 410i, load the config from the disks, and go.  This allows head to
>>> head RAID6 comparison between the P400 and P410i.  No doubt the 410i
>>> will be quicker.  This procedure will tell you how much quicker.
>>
>> Unfortunately, the server is located at a hosting facility at the
>> opposite end of town, and I'd spend an entire day just traveling to
>> and fro, so that's not currently an option. I might get lucky though,
>> because we should soon get another server with an external P410i.
> 
> The new storage blade has only been upgraded to the P410i controller,
> and even though there is a new setting called "elevatorsort", which is
> enabled, the performance is just as bad. The new one has a
> flash-writeback cache and may be faster by a few percent ticks, but
> that's it. It doesn't even make sense to compare the two in-depth, as
> they perform almost identically.

You now have persistent write cache.  Did you test with XFS barriers
disabled?  If not you should.  You'll likely see a decent, possibly
outstanding, performance improvement with your huge metadata
modification workload, as XFS will no longer flush the cache frequently
when writing to the journal log.

-- 
Stan

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