Please show usage on all different levels (fs, snapshots, block, ...)

[testbird]

Btrfs can really be an anoying thing, because it will fill up the disks in multiple different ways, and accordingly there are also multiple different actions to be taken to get out of such locked states.

I found this answer to be the best explanation: https://askubuntu.com/a/464131

I never understood why the btrfs devs do not show in their standard system tools any information about all the different fill up levels involved with btrfs. They get so much negative feedback about this fill up behaviour, and I guess many many users just turn away from btrfs after it absolutely foreseeable --but without any warning-- fills and locks up a device, while the users filesystem is still showing plenty of space, and the usual removing of large files has absolutely no effect because btrfs never removes files but adds a new empty file copy...

You should probably make btrfs-du

• visualize all the fill-up/redundancy levels
• visualize the amount of shadowed-file-versions
• warn about typical misconfigurations like metadata-hogs (cow-logs, DBs, rw-fs-images etc.)
• and point to right balancing/reallocation/snapshot-deletion/cow-defrag/nocow actions, depending on which filling level is closest to 100%.

[testbird]

https://www.suse.com/documentation/sles11/stor_admin/data/trbl_btrfs_volfull.html

[testbird]

https://btrfs.wiki.kernel.org/index.php/Problem_FAQ#I_get_.22No_space_left_on_device.22_errors.2C_but_df_says_I.27ve_got_lots_of_space

[testbird]

https://btrfs.wiki.kernel.org/index.php/FAQ#Help.21_I_ran_out_of_disk_space.21

[testbird]

Uh, standard btrfs reporting is a mess: There is also the GlobalReserve/total that needs to be subtracted from the Metadata/free to know the real available space for metadata (man page).