On Wed 28 Jun 2017 04:58:00 PM CEST, Kashyap Chamarthy wrote: > +Once a 'mirror' job has started, there are two possible actions when a > +``drive-mirror`` job is active: > + > +1. Issuing the command ``block-job-cancel``: will, after completing > + synchronization of the content from the disk image chain to the > + target image, [E] -- create a point-in-time (which is at the time of > + *triggering* the cancel command) copy, contained in image [E], of the > + backing file.
A point-in-time [...] copy [...] of the backing file ? That would be a copy of the whole chain or the topmost image (depending on the sync mode). > +The ``"sync": "full"``, from the above, means: copy the *entire* chain > +to the destination. I think it's in general a good idea to describe the different sync modes before doing this, because they're not completely obvious when you first try to use these commands. > +Notes on ``blockdev-mirror`` > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ [...] > +(1) Create the target image (using ``qemu-img``), say, backup.qcow2 If we're doing a mirror here, backup.qcow2 is probably not the best name :-) > +Live disk backup --- ``drive-backup`` and ``blockdev-backup`` > +------------------------------------------------------------- > + > +The ``drive-backup`` (and its newer equivalent ``blockdev-backup``) allows > +you to create a point-in-time snapshot. > + > +In this case, the point-in-time is when you *start* the ``drive-backup`` > +(or its newer equivalent ``blockdev-backup``) command. > + > +Currently, there are four different types of synchronization modes: > + > +(1) ``full`` -- Synchronize the content of entire disk image chain to > + the target > +(2) ``top`` -- Synchronize only the contents of the top-most disk image > + in the chain to the target > +(3) ``none`` -- Synchronize only the new writes from this point on > +(4) ``incremental`` -- Synchronize content that is described by the > + dirty bitmap Here's the kind of summary of the different sync modes that I was talking about earlier. One note about sync=none, though. If I'm not wrong drive-backup makes a point-in-time copy of the data at the moment when the command is issued (that's one difference from drive-mirror). Therefore drive-backup never synchronizes "new writes from this point on". I don't think that drive-backup sync=none copies any data then, can anyone clarify? The rest of the document looks good to me, thanks! Berto
