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LVM backed drives should default to cache='none'
Binary package hint: virt-manager
KVM guests using LVM backed drives appear to experience fairly high iowait times on the host system if the guest has even a moderate amount of disk I/O. This translates to poor performance for the host and all guests running on the host, and appears to be due to caching as KVM defaults to using writethrough caching when nothing is specified. Explicitly disabling KVM's caching appears to result in significantly better host and guest performance.
This is recommended in at least a few places:
http://<email address hidden>/msg17492.html
http://permalink.gmane.org/gmane.comp.emulators.kvm.devel/48471
http://<email address hidden>/msg30425.html
http://virt.kernelnewbies.org/XenVsKVM
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