@Anthony, I'm aware that I can manipulate the cache settings via libvirt's XML. That's currently what I've been doing, manually after every VM creation. However, my point is that qemu clearly recommends that caching not be used with disks stored on raw volumes. Additionally, virt-manager does not provide any means of disabling caching during or after VM creation. I disagree with your assertion regarding cached IO being faster with KVM. All of my tests indicate a multiple fold increase in performance with caching disabled.
I fail to see how caching provides and more data integrity than no caching. Unless I'm mistaken, no caching provides more integrity by definition. Now, if no caching also provides a mutli-fold performance increase (which it does, as qemu's pages even indicate) why so much resistance to making it the default? -- LVM backed drives should default to cache='none' https://bugs.launchpad.net/bugs/568445 You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. 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/libvir-l...@redhat.com/msg17492.html http://permalink.gmane.org/gmane.comp.emulators.kvm.devel/48471 http://www.mail-archive.com/k...@vger.kernel.org/msg30425.html http://virt.kernelnewbies.org/XenVsKVM
