- Check the integrity of your backup. This is a safe process, but you can always click the wrong button. And read everything once before starting.
- In Partition manager Right click on your btrfs partition
- Edit mount point
- Under Options click the “More…” button
- And type the file system options, comma separated.
- But honestly, just learn to use
/etc/fstab, is a text file, plain and simple.
What this method does is adding an entry to /etc/fstab for you; however, if your partition already has an entry in fstab, it will replace such entry, so in that case it would have been much cleaner to just open fstab in Kate or whatever text editor and append the compress=zstd flag to that entry, Ctrl+S and reboot.
Dolphin does not provide any hint about file system compression.
If you want your whole volume compressed, I would recommend to set the flag and then simply run btrfs fi defrag -v -r -czstd /your/mount/point in a terminal and get done with it. Change zstd for whatever supported compression algorithm you want. In that command, fi stands for filesystem, -v stands for verbose, -r for recursive, and -c for compress.
Take notice that with btrfs, after you set the compress flag, as I’ve already said, only new data will be compressed, unless the volume was mounted with the autodefrag flag (check your fstab file to see what options are in use, unless we are talking about a removable device of course, external devices usually doesn’t have an fstab entry). This is the reason I recommend the command above, it will defrag everything in the volume while compressing it, so you won’t need to wait and see if the autodefrag already worked on X or Y file or haven’t yet.
If you had a btrfs file system, and you add both compress,autodefrag options and reboot, theoretically, any existing data will be compressed the next time it is defraged, however, if the disk isn’t fragmented (which is very likely) it won’t be defraged thus it won’t get compressed. Ergo, defrag manually, and get it over with.