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Re: [virt-tools-list] Default use of caching on raw volumes



Well i just tried this ( i never really did read the documents on that part ) and amazingly my loadavg on the kvm host dropped by a factor of 10.
All the load was coming out of a heavily loaded VM with pgsql in it that was writing all the time ( zabbix monitoring etc. ).
I guess this should really be set as default, not sure if it's up to virt-manager or libvirt.


From: "Jamin W. Collins" <jcollins asgardsrealm net>
To: virt-tools-list redhat com
Sent: Saturday, August 14, 2010 1:16:51 AM
Subject: [virt-tools-list] Default use of caching on raw volumes

If possible I'd like to get some opinions on the following bug report:

https://bugzilla.redhat.com/show_bug.cgi?id=623188

Obviously, I believe that virt-manager should be defaulting to disabling
caching for disks backed by raw volumes as qemu suggests.  There is a
huge performance difference in doing so.  AFAIK, there is no difference,
in terms of risk, between no cache and Writethrough.

I don't quite get Daniel's response and subsequent closing the bug
report indicating that it's a policy decision for virt-manager and the
like.  I filed the report where virt-manager's web site indicated the
report should be filed.

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Nikolai K. Bochev
System Administrator




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