[Libguestfs] Question about using guestfish --ro as a backup solution

It's a bit different from this. What happens is that the libguestfs appliance / kernel attaches to the disk, which is in a potentially unclean *and* potentially changing state. When libguestfs does the mount, the journal recovery is performed (against a throw-away snapshot of the original disk -- if you use the --ro option, the original disk is not written to at all). However the disk is still changing and the libguestfs kernel could interpret this in all sorts of ways: eg. panicking or silently reading corrupt data. The news is: DON'T use guestfish --ro as your backup solution, UNLESS: (1) you don't care about the integrity of your backups, or (2) you can prove that nothing is writing to the disk (eg. the VM is switched off), or (3) you take a snapshot of the disk first (eg. LVM snapshot), which is really just a special case of (2), or (4) the filesystem that you are backing up is frozen[a], which is also a special case of (2). Run a backup daemon inside the guest instead. There are plenty of network backup programs around. Choose your favorite one and install it in your VM. Rich. [a] http://lwn.net/Articles/287435/ -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://et.redhat.com/~rjones/virt-df/