On Fri 22 Jan 2016 09:02:10 PM CET, "Dr. David Alan Gilbert" <address@hidden>
wrote:
In general, what do you do to make sure that the data in a new
Quorum child is consistent with that of the rest of the array?
Quorum can have more than one child when it starts. But we don't
do the similar check. So I don't think we should do such check
here.
Yes, but when you start a VM you can verify in advance that all
members of the Quorum have the same data. If you do that on a
running VM how can you know if the new disk is consistent with the
others?
User error if it is not. Just the same as it is user error if you
request a shallow drive-mirror but the destination is not the same
contents as the backing file. I don't think qemu has to protect us
from user error in this case.
But the backing file is read-only so the user can guarantee that the
destination has the same data before the shallow mirror. How do you
do that in this case?
I think in the colo case they're relying on doing a block migrate to
synchronise the remote disk prior to switching into colo mode.
Yes but this is a general API that can be used independently from
COLO. I'd say if we want to allow that we should at least place a big
warning in the documentation.