On Sun, Sep 19, 2021 at 10:56:58PM +0300, Nir Soffer wrote: > On Mon, Aug 16, 2021 at 6:50 PM Eric Blake <ebl...@redhat.com> wrote: > > > > On Fri, Aug 13, 2021 at 11:55:19PM +0300, Nir Soffer wrote: > > > Both qemu and qemu-img use writeback cache mode by default, which is > > > already documented in qemu(1). qemu-nbd uses writethrough cache mode by > > > default, and the default cache mode is not documented. > > > > > > According to the qemu-nbd(8): > > > > > > --cache=CACHE > > > The cache mode to be used with the file. See the > > > documentation of the emulator's -drive cache=... option for > > > allowed values. > > > > > > qemu(1) says: > > > > > > The default mode is cache=writeback. > > > > > > So users have no reason to assume that qemu-nbd is using writethough > > > cache mode. The only hint is the painfully slow writing when using the > > > defaults. > > > > Oh, good catch. Unfortunately too late for 6.1 proper, but I'll add > > qemu-stable in cc and queue this through my NBD tree for 6.2. > > I don't see this in master, lost in your NBD tree?
It's on my tree: https://repo.or.cz/qemu/ericb.git/shortlog/refs/heads/nbd I just haven't bundled up enough patches for a pull request yet. I'll get one out this week, probably with a few more patches included. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
