The basic idea of btrfs/snapper on the system partition is to undo changes comfortably by ‘snapper rollback’. To do so reliably in case of trouble maintenance is required. It’s done in the background fully automatically by the following services:
**3400G:~ #** systemctl list-timers btrfs* snapper*
NEXT LEFT LAST PASSED UNIT ACTIVATES
Thu 2020-12-03 07:00:00 CET 7min left Thu 2020-12-03 06:00:18 CET 51min ago snapper-timeline.timer snapper-timeline.service
Fri 2020-12-04 00:00:00 CET 17h left Thu 2020-12-03 05:55:32 CET 56min ago btrfs-balance.timer btrfs-balance.service
Fri 2020-12-04 00:00:00 CET 17h left Thu 2020-12-03 05:55:32 CET 56min ago btrfs-defrag.timer btrfs-defrag.service
Fri 2020-12-04 00:00:00 CET 17h left Thu 2020-12-03 05:55:32 CET 56min ago btrfs-scrub.timer btrfs-scrub.service
Fri 2020-12-04 00:00:00 CET 17h left Thu 2020-12-03 05:55:32 CET 56min ago btrfs-trim.timer btrfs-trim.service
Fri 2020-12-04 06:05:34 CET 23h left Thu 2020-12-03 06:05:34 CET 46min ago snapper-cleanup.timer snapper-cleanup.service
**6 timers listed.**
Pass --all to see loaded but inactive timers, too.
**3400G:~ #**
Users failing to monitor background operation for proper execution of these may experience severe issues and need do some manual maintenance. From the information presented above I guess you need to balance manually:
**3400G:~ #** btrfs filesystem usage -T /
Overall:
Device size: 40.00GiB
Device allocated: 22.29GiB
Device unallocated: **17.71GiB**
Device missing: 0.00B
Used: 14.29GiB
Free (estimated): 25.04GiB (min: 25.04GiB)
Data ratio: 1.00
Metadata ratio: 1.00
Global reserve: 43.84MiB (used: 0.00B)
Multiple profiles: no
Data Metadata System
Id Path single single single Unallocated
-- --------- -------- --------- -------- -----------
1 /dev/sda3 21.01GiB 1.25GiB 32.00MiB 17.71GiB
-- --------- -------- --------- -------- -----------
Total **21.01GiB ** 1.25GiB 32.00MiB 17.71GiB
Used 13.68GiB 618.23MiB 16.00KiB
**3400G:~ #** **btrfs balance start -v -dusage=50 /**
Dumping filters: flags 0x1, state 0x0, force is off
DATA (flags 0x2): balancing, usage=50
**Done, had to relocate 3 out of 28 chunks **
**3400G:~ #** btrfs filesystem usage -T /
Overall:
Device size: 40.00GiB
Device allocated: 19.29GiB
Device unallocated: **20.71GiB**
Device missing: 0.00B
Used: 14.29GiB
Free (estimated): 25.04GiB (min: 25.04GiB)
Data ratio: 1.00
Metadata ratio: 1.00
Global reserve: 43.31MiB (used: 48.00KiB)
Multiple profiles: no
Data Metadata System
Id Path single single single Unallocated
-- --------- -------- --------- -------- -----------
1 /dev/sda3 18.01GiB 1.25GiB 32.00MiB 20.71GiB
-- --------- -------- --------- -------- -----------
Total **18.01GiB** 1.25GiB 32.00MiB 20.71GiB
Used 13.68GiB 617.73MiB 16.00KiB
**3400G:~ #**