On 11/13/2011 12:29 AM, Tom Horsley wrote: > I saw a thread a month or so ago on disk performance, and > just for grins, I thought I'd try different disk cache settings > for my Windows XP virtual machine that has a qcow2 image > file (I know qcow2 is never going to be really fast, but I > thought I'd see if I could get any improvement at all). > > Every cache mode I tried (changing them in the advanced > options of the hardware viewer screen in virt-manager) resulted > in the XP machine getting into a bluescreen loop when I booted > it. > > Finally set it back to "default" and the XP machine stopped > getting bluescreens. > > Are other cache modes supposed to work OK? Should I > report a bug on some component? Should I try and capture > the bluescreen content? (It flickers in and out really fast). > > The main reason I was trying this is because it sure seems > like the qcow2 image gets slower and slower every time I > upgrade fedora and get new and improved qemu and libvirt > code. I don't have solid benchmarks, but it sure feels > slower. Has optimization of cases that are supposed to be fast > slowed down qcow2 somehow? > > I'm currently trying to build an updated base image by > doing the trick of writing a giant file of zeros to fill > up the disk so I can then convert the mostly zero image to > a new qcow2 file, and the rate it is going makes it seem like > it may well be tomorrow before it finishes writing the > 10 GB or so of zeros it needs to finish filling up the > disk image. > > None of my CPUs are showing over 1% utilization and gkrellm > is showing only 2.0M disk write rate, so it sure seems like > all the components involved are spending more time just > waiting than anything else.
We need more details - guest/host versions, whether you use virtio or ide, in case of virtio, what's the win pv version, etc. cache=off and cache=writeothrough are safe and pretty much bugfree so I doubt the root cause is there. In addition, latest qcow2 code should perform relatively good, so please provide more details > _______________________________________________ > virt mailing list > [email protected] > https://admin.fedoraproject.org/mailman/listinfo/virt _______________________________________________ virt mailing list [email protected] https://admin.fedoraproject.org/mailman/listinfo/virt
