Timeshift supports BTRFS snapshots, but not backups. A snapshot is taken from the selected BTRFS partition into this partition, not across different partition. In your setup second is the case. I think your system is on another BTRFS partition as your 1TB BTRFS partition on sdb3. If you want to backup BTRFS snapshots then you have to use the combination of btrfs send | btrfs receive. BTRFS it self contains anything to take snapshots and backups to external storages. But Timeshift does’nt support it with BTRFS. Strongly speaking: Timeshift don’t support BTRFS backups, only snapshots on the same partition, and that’s not a real backup. And second: the btrfs snapshots taken with Timeshift are writeable snapshots to my knowledge, that’s a realy bad idea of a snapshot.
Thus i suggest to use another toolchain for btrfs snapshots and backups. Take a look onto follow combination:
- Snapper + Snapper GUI to take ro-snapshots, with automated cleanup algorithms
- snap-pac to automatically make snapshots with Snapper before and after installation of packages from repository and AUR
- grub-btrfs to automatically update GRUB with boot menuentries to boot into Snapper ro-snapshots
- snap-sync to automatically make differential backups of Snapper snapshots to external btrfs formated storages, through ssh-tunnels.
- right setup of BTRFS to support UEFI, root snapshots with included kernel + library (/var/lib) snapshots, bootable ro-snapshots of the entire system into DE/GUI.
I use above combination on 5 machines running Manjaro. One of them have attached a USB3 SATA SSD which holds the btrfs backup partition. Daily differential full system backups with SSH tunnels take about 5-10 seconds, and that’s the advantage of btrfs, if correctly used.