[openstack-dev] [nova] Feature about QEMU Assisted online-extend volume
zhangleiqiang at gmail.com
Thu Mar 27 16:15:54 UTC 2014
Online-extend volume feature aims to extend a cinder volume which is
in-use, and make the corresponding disk in instance extend without stop the
The background is that, John Griffith has proposed a BP () aimed to
provide an cinder extension to enable extend of in-use/attached volumes.
After discussing with Paul Marshall, the assignee of this BP, he only focus
on OpenVZ driver currently, so I want to take the work of libvirt/qemu
based on his current work.
A volume can be extended or not is determined by Cinder. However, if we
want the capacity of corresponding disk in instance extends, Nova must be
Libvirt provides "block_resize" interface for this situation. For QEMU, the
internal workflow for block_resize as follows:
1) Drain all IO of this disk from instance
2) If the backend of disk is a normal file, such as raw, qcow2, etc, qemu
will do the *extend* work
3) If the backend of disk is block device, qemu will first judge if there
is enough free space on the device, if only so, it will do the *extend*
So I think the "online-extend" volume will need QEMU Assisted, which is
simlar to BP .
Do you think we should introduce this feature?
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