Writeback Stalls

[Emmanuel Florac]

Le Wed, 19 Sep 2012 18:36:11 +0000 vous écriviez:

> We have an small sized VMWare infrastructure. 8 hosts with round
> about 50 VMs. Their images are hosted on 2 Ubuntu 12.04 NFS storage
> servers with each of them having a 14 disk RAID 6 array. On top of
> the array runs a single XFS filesystem with round about 10TB of disk
> space.

You didn't mention the type of disks and controllers you're using, it
makes a very important difference. Typically in VM environment RAID-6
on 7200RPM drives behaves quite poorly because of very poor random IO
write performance. 
You should also look at the iostat -mx output on the NFS server.
You'll probably see a 100% disk usage with lots of small read and write
IOs.

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