Hi there,
Kernel: 5.7.8
btrfs-progs 5.7
Noticed that df reports the wrong free space when used on a raid1
btrfs pool with an odd number of devices, e.g.:
2 x 500GB (correct)
Filesystem Size Used Avail Use% Mounted on
/dev/sdd1 466G 3.4M 465G 1% /mnt/cache
3 x 500GB (not correct)
Filesystem Size Used Avail Use% Mounted on
/dev/sdd1 699G 3.4M 466G 1% /mnt/cache
btrfs fi usage -T /mnt/cache
Overall:
Device size: 1.36TiB
Device allocated: 4.06GiB
Device unallocated: 1.36TiB
Device missing: 0.00B
Used: 288.00KiB
Free (estimated): 697.61GiB (min: 697.61GiB)
Data ratio: 2.00
Metadata ratio: 2.00
Global reserve: 3.25MiB (used: 0.00B)
Multiple profiles: no
Data Metadata System
Id Path RAID1 RAID1 RAID1 Unallocated
-- --------- ------- --------- -------- -----------
1 /dev/sdd1 - 1.00GiB 32.00MiB 464.73GiB
2 /dev/sdg1 1.00GiB - - 464.76GiB
3 /dev/sdb1 1.00GiB 1.00GiB 32.00MiB 463.73GiB
-- --------- ------- --------- -------- -----------
Total 1.00GiB 1.00GiB 32.00MiB 1.36TiB
Used 0.00B 128.00KiB 16.00KiB
Same for 5 devices and I assume any other odd number of devices:
5 x 500GB
Filesystem Size Used Avail Use% Mounted on
/dev/sdd1 1.2T 3.4M 931G 1% /mnt/cache
btrfs fi usage -T /mnt/cache
Overall:
Device size: 2.27TiB
Device allocated: 4.06GiB
Device unallocated: 2.27TiB
Device missing: 0.00B
Used: 288.00KiB
Free (estimated): 1.14TiB (min: 1.14TiB)
Data ratio: 2.00
Metadata ratio: 2.00
Global reserve: 3.25MiB (used: 0.00B)
Multiple profiles: no
Data Metadata System
Id Path RAID1 RAID1 RAID1 Unallocated
-- --------- ------- --------- -------- -----------
1 /dev/sdd1 - - 32.00MiB 465.73GiB
2 /dev/sdg1 - 1.00GiB - 464.76GiB
3 /dev/sdb1 - - 32.00MiB 465.73GiB
4 /dev/sde1 1.00GiB 1.00GiB - 463.76GiB
5 /dev/sdf1 1.00GiB - - 464.76GiB
-- --------- ------- --------- -------- -----------
Total 1.00GiB 1.00GiB 32.00MiB 2.27TiB
Used 0.00B 128.00KiB 16.00KiB
Is this a known issue, and if not would it be a btrfs or df problem?
Thanks,
Jorge
