Re: [Qemu-devel] tcmu-runner and QEMU

[Stefan Hajnoczi]

On Thu, Sep 04, 2014 at 08:15:39AM -0700, Andy Grover wrote:
> But in the meantime, do you have a use case or user story for the QMP
> support that might help me understand better how it might all fit together?

From my previous email:

"administrator needs to migrate disk images to a new file system or
storage devices without downtime."

Here is some more detail about how that works:

QEMU has a drive-mirror QMP command that copies the disk image to a new
location while continuing to service I/O.  In other words live storage
migration, no downtime.

A tool needs to connect to the QMP unix domain socket and issue the
drive-mirror command.  Then it needs to wait until the QMP events are
raised signalling drive-mirror completion and it block-job-complete QMP
command to atomically switch to the new image file (it is now safe to
delete the old image file).

Stefan

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