Launchpad has imported 5 comments from the remote bug at https://bugzilla.redhat.com/show_bug.cgi?id=623188.
If you reply to an imported comment from within Launchpad, your comment will be sent to the remote bug automatically. Read more about Launchpad's inter-bugtracker facilities at https://help.launchpad.net/InterBugTracking. ------------------------------------------------------------------------ On 2010-08-11T14:43:39+00:00 Jamin wrote: Description of problem: Defaults to using cache with an LVM backed storage. The use of caching with raw partitions (LVM) results in significantly lower performance than no cache at all. How reproducible: Always Steps to Reproduce: 1. Create a new VM using LVM backed storage Actual results: Cache is enabled for the VM's disks residing within LVM. Expected results: Cache should be disabled for disks residing within LVM. Additional info: http://www.linux-kvm.org/page/Tuning_KVM Specifically: QEMU also supports a wide variety of caching modes. Writeback is useful for testing but does not offer storage guarantees. Writethrough (the default) is safer, and relies on the host cache. If you're using raw volumes or partitions, it is best to avoid the cache completely, which reduces data copies and bus traffic: qemu -drive file=/dev/mapper/ImagesVolumeGroup- Guest1,cache=none,if=virtio This has also been reported with Ubuntu at: https://bugs.launchpad.net/ubuntu/+source/virt-manager/+bug/568445 Reply at: https://bugs.launchpad.net/ubuntu/+source/virt- manager/+bug/568445/comments/12 ------------------------------------------------------------------------ On 2010-08-11T16:12:46+00:00 Daniel wrote: Choice of caching mode is a policy decision. These belong in virt- manager or other apps using libvirt. Reply at: https://bugs.launchpad.net/ubuntu/+source/virt- manager/+bug/568445/comments/13 ------------------------------------------------------------------------ On 2010-08-11T17:01:21+00:00 Jamin wrote: AFAIK, this is the place to post feature requests for virt-manager, at least this is where their website directed me. Intentionally selecting a default mode that results in very poor performance (about 1/5 less) when the upstream for the virtualization engine (qemu/kvm) clearly indicates that another mode is preferable is (IMHO) a bad choice. Furthermore, from what I can tell, virt-manager doesn't appear to provide any means of changing or overriding the default. A user must instead manually edit the server's XML definition of the VM in question. Reply at: https://bugs.launchpad.net/ubuntu/+source/virt- manager/+bug/568445/comments/14 ------------------------------------------------------------------------ On 2010-08-16T15:38:49+00:00 Jamin wrote: Reopening against virt-manager as recommended on mailing list. Reply at: https://bugs.launchpad.net/ubuntu/+source/virt- manager/+bug/568445/comments/18 ------------------------------------------------------------------------ On 2013-10-02T20:12:51+00:00 Cole wrote: Fixed upstream now Reply at: https://bugs.launchpad.net/ubuntu/+source/virt- manager/+bug/568445/comments/20 ** Changed in: virt-manager Status: Unknown => Won't Fix ** Changed in: virt-manager Importance: Unknown => Medium -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/568445 Title: LVM backed drives should default to cache='none' Status in QEMU: Invalid Status in virt-manager: Won't Fix 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-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 To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/568445/+subscriptions
