[libvirt] [PATCH] Add "io" option to virsh attach-disk sub-command.

Daniel P. Berrange berrange at redhat.com
Tue May 9 14:38:56 UTC 2017

On Tue, May 09, 2017 at 07:31:30AM -0700, Gordon Messmer wrote:
> (Apparently I managed to screw up sending that, twice.   Long weekend.)

No problem. Your first posting got blocked into the moderator queue
since you weren't a subscriber. One of the list admins then approved
it, not realizing you had already subscribed to the list & resent the

> Please consider adding the option of setting the "io" attribute when
> attaching disks to guests.  Under Red Hat (unsure if this is true under
> vanilla libvirt), virt-install and virt-manager both default to explicitly
> setting "io='native'" in the disk "driver" tag. virsh, however, does not and
> also does not provide an option to specify that setting at all.  As a
> result, disks use a different IO mechanism (the default, "threads") when
> attached post-setup using virsh.  Adding this option allows users to keep
> disk performance consistent for disks attached at install, and those
> attached afterward.

I think you can use the --iothread flag to "virsh attach-disk" to set
this parameter. virsh doesn't set it if not specified, since it tries
to avoid making policy decisions, like virt-manager/virt-install do

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