[pve-devel] Live storage migration V2

[Fabian Grünbichler]

On Thu, Oct 20, 2016 at 02:35:09AM +0200, Alexandre Derumier wrote:
> changelog:
>  - add support for multiple local disks
>  - complete the mirror jobs after the vm migration
>  - rewrote qemu-mirror block jobs monitoring to handle multiple jobs in parralel
>  - qm migrate <vmid> <targetnode> -online will try to use same disks storeid && format for remote local
>    you can add -targetstorage  to choose alternative remote storage
>  - stop nbd server at the end of the migration
>  - lot of cleanups

a general question as I am unsure about this - would it make sense to
move from the current binary switch (--online or not) to a mode option
like we have for vzdump?

if we reuse the online flag for this new backup mode, it would be a big
departure from the current semantics (online is only for shared storage,
nothing except the config file and RAM is migrated). this might confuse
users and lead to unexpected results (e.g., because of the additional
load/latency caused by disk mirroring).

it would also make future introduction of new backup modes easier and
less confusing (there is at least one zfs send/receive based one that I
can think of).

on the GUI side we could probably preselect the most appropriate one:
- old style online if VM is running and completely shared
- new style online if VM is running and has local disks
- offline if VM is not running

if neither mode nor online is set, the default would still be offline
if only online is set, the old style online would be used
if both are set, display a descriptive error message

of course, such a mode switch would require meaningful (and ideally,
futureproof) names for the modes ;)