[Bug 568445] [NEW] LVM backed drives should default to cache='none'

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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://www.mail-archive.com/libvir-list@redhat.com/msg17492.html
http://permalink.gmane.org/gmane.comp.emulators.kvm.devel/48471
http://www.mail-archive.com/kvm@vger.kernel.org/msg30425.html
http://virt.kernelnewbies.org/XenVsKVM

** Affects: qemu-kvm (Ubuntu)
     Importance: Undecided
         Status: New

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LVM backed drives should default to cache='none'
https://bugs.edge.launchpad.net/bugs/568445
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