[libvirt] PATCH: Disable QEMU drive caching

Daniel P. Berrange berrange at redhat.com
Wed Oct 8 16:42:42 UTC 2008

On Wed, Oct 08, 2008 at 10:51:16AM -0500, Anthony Liguori wrote:
> A great deal of virtualization users are doing some form of homogeneous 
> consolidation.  If they have a good set of management tools or 
> sophisticated storage, then their guests will be sharing base images or 
> something like that.  Caching in the host will result in major 
> performance improvements because otherwise, the same data will be 
> fetched multiple times.

NB, this has no impact on caching of backing files - QEMU masks out
the O_DIRECT flag when opening the backing file - so in a shared
master image scenario, all reads for the shared file will still be 
cached, only write5Cs to the cow file are impacted.

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