Re: [Qemu-devel] [RFC] lively write vmstate with predictable size

[Eric Blake]

On 01/05/2013 01:21 AM, Wenchao Xia wrote:
>   I guess migration to file makes vm stopped, and lack a step
> to take snapshot in the end of migration, also the usage seems
> strange makes me feel something is lacking. I'd like to
> have:
> 1 take blk snapshot internal/external lively.
> 2 take vmstate snapshot internal/external lively.
> 3 combination.

Libvirt 1.0.1 can already do external live snapshots - it does a live
migration to file, and when that finally converges enough to pause,
there is less than a second of downtime when libvirt then follows up
with an external disk snapshot and then resumes the guest.  Of course,
this approach requires multiple files, and there is no way to take an
internal snapshot with current QMP support.  And the point remains in
this thread that a live migration to file takes more space than a paused
migration, in part because earlier portions of the migration stream are
revisited later in the stream as memory pages continue to be touched
during the live migration.  So a new format for seekable migration to
file, different than current migration being usable over a fifo, may
indeed allow for less disk space and faster booting when reverting to
that vmstate.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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