[Qemu-devel] [Bug 568445] Re: LVM backed drives should default to cache='none'

[Anthony Liguori]

cache=writethrough and cache=none have equivalent data integrity.

FWIW, I believe most recent versions of virt-manager default to
cache=none for physical devices.

-- 
LVM backed drives should default to cache='none'
https://bugs.launchpad.net/bugs/568445
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Status in QEMU: Invalid
Status in “virt-manager” package in Ubuntu: Triaged

Bug description:
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/address@hidden/msg17492.html
http://permalink.gmane.org/gmane.comp.emulators.kvm.devel/48471
http://www.mail-archive.com/address@hidden/msg30425.html
http://virt.kernelnewbies.org/XenVsKVM