I’d like to compare any changes between a running instance and a snapshot but there’s some issues. The instance is a virtual machine, and zfs shows it to be of the type volume. Because it’s a volume type, there isn’t a mountpoint to set. And /dev doesn’t seem to show any block devices that i can try accessing.
How can i do a diff between a vm instance and a snapshot if i cannot mount the block device ?
Easiest is to lxc copy name/snapshots old-name so you get a new instance from that snapshot, then you can start it and compare things between the two. You may want to remove the network interface from old-name though to avoid it conflicting with the current version of the instance.
Isn’t it possible to mount the zfs block type somehow? Or someway of accessing the storage directly?
You can do a zfs set volmode=full name/of/dataset which will make some /dev/zvol entries show up. However I don’t believe you can do that on a snapshot, so you’ll still need to make a copy.
Doesn’t the lxc snapshot use the zfs snapshotting capability? Meaning there’s a snapshot dataset that is mountable?
Yeah, LXD snapshots create a ZFS snapshot. But for a VM, this means a snapshot on a ZFS volume, so not something you can mount directly, it’s a big binary block device with partitions and such.
A vm snapshot can be mounted if snapdev=visible is set additionally.
Altogether:
lxc snapshot mytestvm backup
zfs set volmode=full tank/virtual-machines/mytestvm.block
zfs set snapdev=visible tank/virtual-machines/mytestvm.block
mount /dev/zvol/tank/virtual-machines/mytestvm.block\@snapshot-backup-part2 /mnt/mytestvm.block