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Re: A little RAID experiment

To: Roger Willcocks <roger@xxxxxxxxxxxxxxxx>
Subject: Re: A little RAID experiment
From: Stefan Ring <stefanrin@xxxxxxxxx>
Date: Thu, 26 Apr 2012 10:53:50 +0200
Cc: Linux fs XFS <xfs@xxxxxxxxxxx>
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In-reply-to: <1335363423.4586.431.camel@xxxxxxxxxxxxxxxxxxxxxxxx>
References: <CAAxjCEzh3+doupD=LmgqSbCeYWzn9Ru-vE4T8tOJmoud+28FDQ@xxxxxxxxxxxxxx> <1335363423.4586.431.camel@xxxxxxxxxxxxxxxxxxxxxxxx>
> Read 0b  Written 995.77Mb  Total transferred 995.77Mb  (66.337Mb/sec)
>  8491.11 Requests/sec executed]

I was a bit sceptical towards your measurement at first, especially
since your xfs_bmap shows that the file is split into 4 regions which
nicely aligns (almost) with the agcount=4 setup that the benchmark
emulates, but this seems to be just a coincidence.

Meanwhile, I've found a customer's system, where we have a MegaRAID
SAS 1078 with a 6-disk RAID 6 volume, and this one delivers 54MB/sec,
which really puts the SmartArray controller to shame at its measly
4MB/sec.

I just want to stress that our machine with the SmartArray controller
is not a cheap old dusty leftover, but a recently-bought (December
2011) not exactly cheap Blade server, and that’s all you get from HP.

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