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[Xen-users] 100% iowait in domU with no IO tasks.

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] 100% iowait in domU with no IO tasks.
From: "Bogdan B. Rudas" <brudas@xxxxxxxxxxx>
Date: Thu, 8 May 2008 12:02:30 +0300
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I entered one of our domU tonight and see following problem: 

# iowait -k 5

avg-cpu:  %user   %nice %system %iowait  %steal   %idle

           0.00    0.00    0.00  100.00    0.00    0.00

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda1              0.00         0.00         0.00          0          0
sda2              0.00         0.00         0.00          0          0

I check other domU and dom0 on same server - there were high iowait: from 20% 
to 50% with few transactions per second and about 0.1-1.5 Mb/sec storage 
bandwith usage per domU. This domU have no disk IO at all but show LA 15 and 
possible higher.

We have 6 domU on 8-core server with 7 FUJITSU  MBB2147RC SAS HDD on DELL PERC 
5/i RAID controller.

CentOS 5
Xen 3.1.0
Kernel 2.6.21

We suffer from this problem for a while on many our xen hosts, it is not a 
single-time issue.

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