Re: [libvirt] [Qemu-block] [RFC] finegrained disk driver options control

On Thu 16 Mar 2017 04:08:50 PM CET, Daniel P. Berrange wrote: >> OK. How could I change L2 cache size for QCOW2 image? >> >> For 1 Tb disk, fragmented in guest, the performance loss is >> around 10 times. 10 TIMES. 1000%. The customer could not >> wait until proper fix in the next QEMU release especially >> if we are able to provide the kludge specifically for him. > We can explicitly allow L2 cache size set in the XML but that > is a pretty poor solution to the problem IMHO, as the mgmt > application has no apriori knowledge of whether a particular > cache size is going to be right for a particular QCow2 image. > > For a sustainable solution, IMHO this really needs to be fixed > in QEMU so it has either a more appropriate default, or if a > single default is not possible, have QEMU auto-tune its cache > size dynamically to suit the characteristics of the qcow2 image. Related bug report (and discussion): https://bugzilla.redhat.com/show_bug.cgi?id=1377735 Berto