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[Xen-users] Slow disk writes on domu.

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Slow disk writes on domu.
From: John McMonagle <johnm@xxxxxxxxxxx>
Date: Mon, 9 May 2011 07:28:54 -0500
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Seen a couple threads on this but saw no resolution.

I'm seeing the problem on all but one system.

For all tests dom0 and domu are debian squeeze with debian 2.6.32 xen kernel.
Xen is 4.1.0
testing with 
dd if=/dev/zero of=test bs=1M count=1000

Problem system
dom0  39.0 MB/s
domu  13.4 MB/s
There was some usage on other domus but results were consistent.
smaller writes look good  probably because of buffering.
A 100mb write on domu is 74.2 MB.

Good system.
dom0  45.1 MB/s
domu  66.4 MB/s
Oddly domu was always a little faster.

There are many hardware differences but the one thing I can see is the faster 
one is the only server with hardware raid.
It seems odd to me that mdadm raid 1 would have much of a negative affect.


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