Timeshift btrfs snapshots showing size in bytes


I’m having a weird issue with Timeshift on a btrfs filesystem. I’m using two different SSD drives, one with the /boot/efi, root (/) and swap partitions, and another for /home partition. I formatted the root partition and home partition with btrfs.

Upon entering my newly installed system, I noticed that Timeshift was only taking snapshots of the root partition, leaving the /home partition without snapshots, so I researched a little and decided create a btrfs subvolume called @home on the /home partition (on a different SSD) to enable Timeshift to take snapshots of my /home.

After doing all the required changes (from a LiveUSB, creating the subvolume, copying the user folder into @home directory, edit fstab to include subvol=@home in the correct partition, rebooting, running chown user:group -R /home/), Timeshift can now see my /home partition and take snapshots of both partitions, but the size of the previous and current snapshots look weird:

Shouldn’t the size column show sizes in GB? I could swear this was the case before doing all the changes to my /home partition, maybe my eyes are playing tricks on me? I’ve ran du -sh on all the snapshots and they are showing the expected sizes.

What you need to understand is that btrfs is a copy-on-write filesystem, and that a snapshot of a particular subvolume is therefore not a copy of said subvolume. Extents ─ i.e. the equivalent of filesystem blocks ─ that have not been modified are not copied over but are instead only linked to in the btrfs extent allocation layer.

If you want to use timeshift for creating full and incremental backups, then I recommend using it in rsync mode, with the backups stored on a separate drive. Then there will also be linking going on for the unmodified files, but this will be against an integral physical copy of the files.

Ok, so this is normal and my eyes were definitely playing tricks on me.

Right now I only want to use timeshift for the easiness of going back if something goes wrong, and using rsync would defeat the purpose of having btrfs partitions, if I’m not mistaken. For full backups I’m planning on using some other solution, I’m still looking into the possibilities.

Anyway, thank you for the quick reply!

No, that is not correct. They are two very different things. :wink:

Wait, I think I understand what you’re saying. I can use both modes with timeshift and change between them, correct?

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Yes, that is correct. :slight_smile:

That’s awesome, I don’t know why I didn’t figured that out before. Yes, then having btrfs partitions is definitely a plus, since I can have both the speed of btrfs snapshots and the flexibility of rsync to save on any drive.

Thank you for the information! :slightly_smiling_face:

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