Backup from restic-mount for cascading backup

Is it a good idea to create a backup from a mounted snapshot?

I would like to setup a cascading backup where I save the directories A, B, C to an external disk, B, C to an internal disk and C to a external server. The best would be to create the backup for the external disk and derive from this the snapshots for the internal disk and the server.

But currently restic doesn’t support exporting snapshots to other repositories. So I thought to mount the snapshot of the external disk and create the backup for the other two from this. Is this a good and performant idea?

I don’t see why it wouldn’t work, but my experience with restic mount is that it’s fairly slow, so it may not be that performant. You could always try and see how well it works.

In particular I’d be interested to see if the generated root tree has the same ID as in the original snapshot. My suspicion is that it would not since fuse filesystems don’t retain inode IDs.