@rfx77 Thanks for clarifying my question, your reading of it was correct.
I've just realized that syncoid has an option, --no-sync-snap, which I think avoids creating a dedicated snapshot for the purpose of the transfer, and instead just transfers over the pre-existing snapshots. If that's indeed what it does, then this solves all potential problems, because the existing snapshots are taken from xen-orchestra. I'll do a test to confirm this is indeed the behavior and then will reply again.
A question or point about the SMAPIv3 ZFS driver. I had a power failure in my testing lab last week and I noticed that the VMs with SMAPIv3 disks attached did not come back up automatically, despite being set to automatically power on. Perhaps this is related to the ZFS driver? My first thought was that there might be a race condition between the VM start and the zpool import at boot up but I don't know how to verify that.
I just figured I would report this in case it's useful to anyone at Vates.
@cg sorry if this is off topic but do you know of any HW raid controllers which actually do this? Storing checksums or whatever?
@rfx77 thanks for the recommendations. I looked into zrepl and it seems like a good solution as well. However, since I'm using this new zfs beta driver in production, I've decided I'm going to do the backup at the VM filesystem level, i.e. with rsync, instead of at the ZFS level. I figure that strategy is slightly safer in the event of bugs with the driver. I know that's debatable - it would depend on the bug, but this approach feels safer to me.
@rfx77 Thanks for clarifying my question, your reading of it was correct.
I've just realized that syncoid has an option, --no-sync-snap, which I think avoids creating a dedicated snapshot for the purpose of the transfer, and instead just transfers over the pre-existing snapshots. If that's indeed what it does, then this solves all potential problems, because the existing snapshots are taken from xen-orchestra. I'll do a test to confirm this is indeed the behavior and then will reply again.
I've started using the SMAPIv3 driver too. It's working well so far. I'm keeping my VM boot disks on md raid1, and using a zfs mirror via SMAPIv3 for large data disks.
I have a question about backups... Is it safe to use syncoid to directly synchronize the ZFS volumes to an external backup? syncoid creates a snapshot at the start of the send process. But, I also have rolling snapshots configured through Xen-Orchestra. Will the syncoid snapshot mess up Xen-Orchestra?
If this isn't safe or isn't a good idea, I'll just use rsync to back up the filesystem contents inside the VM that the volume is mounted to...