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

[Nikolai K. Bochev]

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 at asgardsrealm.net> 
To: virt-tools-list at 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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