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

Thomas Fjellstrom tfjellstrom at shaw.ca
Fri Aug 20 09:00:41 UTC 2010

>On 08/18/2010 09:23 AM, Daniel P. Berrange wrote:
>> Previously when anyone has suggested setting cache=none for QEMU,
>> other people have appeared with test results showing that other
> Care to provide references?  I've yet to find a single report where 
> caching provides better performance with VMs stored on raw volumes 
> except for the use of writeback which is not recommended for anything 
> where data integrity is concerned.  My suggested change improves 
> performance without risking data integrity.

After seeing this thread I tried to see what would happen with a windows xp 
guest using lvm+virtio and changing the cache option to none. Performance 
drops about 10-20MB/s. Whatever the default is, I get an average of 55MB/s 
read according to hd-tune. With cache=none I get more like 35-40MB/s.

Thomas Fjellstrom
tfjellstrom at shaw.ca

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