backups of bhyve images

[Peter Grehan]

Hi John,

> Basically, what I want to do is to run accurate backups without shutting
> down and restarting the VM. Is this possible? If it isn't, I think the
> only alternative is to make a script that shuts the vm down, copies it,
> restarts the vm then runs its compression and backup-over-ssh routine.

  It's not possible in the general case to take a snapshot of the 
underlying image since as others have pointed out, it may not be 
consistent on disk since there are still data/metadata from the guest's 
filesystem that haven't made it out to disk.

  Commercial hypervisors provide guest tools that allow a filesystem 
quiesce/sync that lock-steps with external snapshotting machinery.

  However, one option that could be worth investigating is using ZFS in 
the guest with disk images backed by a zvol on the host. ZFS guarantees 
on-disk consistency, and a zvol provides instantaneous snapshots. Worst 
case is that some writes are not picked up at snapshot time, but that 
seems preferable to having to force a full sync in the guest.

later,

Peter.