Il 28/01/2013 11:01, Kevin Wolf ha scritto: > Am 27.01.2013 22:21, schrieb Tom Horsley: >> Back around fedora 16 I tried all the different virtio >> cache modes and experimentally discovered that >> cache=none was nearly infinitely faster than cache=default >> and cache=writeback was even a little faster than cache=none. >> So I set all my VMs to cache=writeback. >> >> I've been copying my virtual machine defs to each new >> fedora since then, but now it seems to be dog slow >> with disk IO again. >> >> I'm planning to experiment with different settings again, >> but I have to wait for my Windows XP virtual machine >> to finish doing a windows update which may take all night >> at the rate it is writing to disk :-(. >> >> Just thought I'd ask if there is some known difference >> in the virtio modes in fedora 18? > > One thing that is relatively new, and might not have been in F17, is > that virtio-blk automagically enables a writethrough mode if the guest > doesn't advertise that it supports flushes. If this is the case, you > actually get cache=directsync instead of cache=none, which obviously > hurts performance, but ensures that your image doesn't get corrupted on > a crash. > > I don't think there is an option to override this magic, except maybe > cache=unsafe.
Yes, cache=unsafe will override it. Paolo _______________________________________________ virt mailing list [email protected] https://admin.fedoraproject.org/mailman/listinfo/virt
