Re: [libvirt] PATCH: Disable QEMU drive caching
Daniel P. Berrange wrote:
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
It doesn't mask out O_DIRECT, it just doesn't pass any flags to the
backing file when it opens it. IMHO, this is a bug.
Regards,
Anthony Liguori
- 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.
Daniel