On 05/16/2017 11:00 AM, Markus Armbruster wrote: >>>> # periodic mode. (Since 2.8) >>>> # >>>> +# @block-incremental: enable block incremental migration (Since 2.10) >>>> +# >>> >>> What's "block incremental migration" and why should I care? >> >> This is good, I will try. >> >> "block incremental migration assumes that we have a base image in both >> sides, and then we continue writting in one of the sides. This way we >> need to only migrate the changes since the previous state where it was >> the same in both sides". >> >> I am not sure what to put there, really. > > Well, to suggest something, I'd first have to figure out WTF incremental > block migration does. Your text helps me some, but not enough. What > exactly is being migrated, and what exactly is assumed to be shared > between source and destination? > > Block migration is scandalously underdocumented.
If I have: base <- active on the source, then: block migration without incremental creates: active on the destination (the entire disk contents are migrated). Conversely, block migration WITH incremental assumes that I have pre-created 'base' on the destination (easy to do, since base is read-only so it can be copied prior to starting the migration), and the migration results in: base <- active on the destination, where only the contents of active were transferred by qemu. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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