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Shared NFS Disk causing high Wait CPU on dd command

733736Nov 23 2009 — edited Nov 26 2009

Hi,

we have mounted the partition /OVS to a NFS shared disk, and we are running a virtual machine from this shared disk.

Doing the following command in the virtual machine, we calculate the needed time to write a file into the NFS disk with block size = 1M. We also tried with different block sizes.

time dd if=/dev/zero of=/tmp/1GB.test bs=1M count=1024
1024+0 records in
1024+0 records out

real 0m4.085s
user 0m0.000s

If we check the Virtual Machine CPU Usage during this process, Wait CPU time highly increases as we show below (doesn't matter the block size)

!http://img69.imageshack.us/img69/7651/highwaitcpu.th.png!
http://img69.imageshack.us/i/highwaitcpu.png/

In the other hand, executing the same command in a local disk, Wait CPU is really low and normal.

Is a NFS issue? Is the right way to work? Do we have a wrong Virtual Machine configuration?

Thanks in advance,
Marc

Edited by: Marc Caubet on Nov 23, 2009 8:20 AM

Edited by: Marc Caubet on Nov 23, 2009 8:20 AM

Edited by: Marc Caubet on Nov 23, 2009 8:21 AM

This post has been answered by Herbert van den Bergh-Oracle on Nov 26 2009

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#oracle-virtualization, #oracle-vm-server-for-x86

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