Explore backups for fixed LVM, non-CoW storage

[tasket]

Many systems are installed with fixed (non-thin) lvm volumes and documentation suggests thin snapshots can be created for fixed volumes. If so, it may be possible to use the thin lvm tools to track deltas for fixed volumes the same way as in an all-thin environment.

The challenges for implementation are:

• Determining actual thin-tools compatibility with these hybrid snapshots.
• Tracking the fixed nature of configured volumes during archive ops, if any special steps are needed.
• Advising users on a straightforward way to configure their fixed-lvm system with a suitable thin pool.

Barring the above, it may be helpful to reference documentation showing the best practices for converting fixed-lvm systems over to thin pools, btrfs, etc.

[tasket]

After researching hybrid snapshots, there is no way to target a non-thin vol + thin snapshot consistently since the non-thin volume's state cannot be known from its metadata. The combination could easily be corrupted and Wyng would have no way to detect or compensate for it.

So I'm changing this issue to a general 'Support volumes in non-snapshot storage' theme. Such volumes would have to be added to the archive with a special option flagging them as non-CoW, and they would essentially trigger a --remap on each incremental send. IOW, this volume type could be supported if Wyng treated it like a traditional incremental backup, comparing all the volume data against hashes for each run.

Users should be consistently reminded of this special mode to prevent confusion about slower backup times, etc.

[tasket]

Some support for this can be added via an option like --import-from to enable reading volumes that sit outside of a supported snapshot storage system. This would complement the existing --save-to option.

[tasket]

@tlaurion Implemented option --import-other-from which is to be used like this:

wyng send --import-other-from=volname:|:path/to/file

The char sequence ':|:' is used as a delimiter between the archive volume name and the source file path.

This requires testing.

[tlaurion]

@tlaurion Implemented option --import-other-from which is to be used like this:

wyng send --import-other-from=volname:|:path/to/file

The char sequence ':|:' is used as a delimiter between the archive volume name and the source file path.

This requires testing.

@tasket i tried to test this today through wyng-util-qubes -w import-other-from=boot:|:/dev/sda1 without success. Not sure what I'm missing.