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Re: [Xen-users] Physical Disk VBD vs File VBD Performance

To: m0topilot@xxxxxxxxx
Subject: Re: [Xen-users] Physical Disk VBD vs File VBD Performance
From: "Michael T. Babcock" <mike@xxxxxxxxxxxxxx>
Date: Wed, 05 Sep 2007 13:56:40 -0400
Cc: xen-users Group <xen-users@xxxxxxxxxxxxxxxxxxx>
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Matias wrote:
Correct me if I'm wrong, when writing
to RAID5 the data gets striped up and your write performance increases.
Now if I write to the dom2 it has to write the whole data to one spindle.

RAID5 frequently causes performance losses, not gains, although with high performance controllers and disks you can see performance improvements over a raw disk. The problem is that the data isn't just striped like in a RAID-0 set, the data has to have parity information calculated and written out as well, and all disks get hit with write requests at the same time when writing out data. On reads (in a non-degraded set), you may see performance increases because of the striped nature of the data, but no guarantees.
Michael T. Babcock

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