how to recover from "enospc errors during balance"

[Giovanni Biscuolo <g@xelera.eu>]

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Hello,

please also reply to me since I'm not subscribed to linux-btrfs, thanks!

My BTRFS filesystem is full, I got ENOSPC during a (scheduled) balance:

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[6928066.755704] BTRFS info (device sda3): balance: start -dusage=50 -musage=70 -susage=70
[6928066.760485] BTRFS info (device sda3): relocating block group 139449073664 flags metadata|raid1
[6928075.142462] BTRFS: error (device sda3) in btrfs_drop_snapshot:5421: errno=-28 No space left
[6928075.146566] BTRFS info (device sda3): forced readonly
[6928075.150851] BTRFS info (device sda3): 2 enospc errors during balance
[6928075.155422] BTRFS info (device sda3): balance: ended with status: -30
[6928083.483820] BTRFS info (device sda3): delayed_refs has NO entry

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and now it's mounted read-only:

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/dev/sda3 on / type btrfs (ro,relatime,ssd,space_cache,subvolid=5,subvol=/)
/dev/sda3 on /gnu/store type btrfs (ro,relatime,ssd,space_cache,subvolid=5,subvol=/gnu/store)

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If I try to remount rw (to try to free space) I get:

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[7323937.312122] BTRFS info (device sda3): disk space caching is enabled
[7323937.316478] BTRFS error (device sda3): Remounting read-write after error is not allowed

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I tried to add a new device (I have 2 spare disks) but it does not work
with a read-only filesystem.

Please how can I remount the filesystem read-write and free some space
deleting some files?

Additional data:

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~$ uname -a
Linux myhost 5.4.50-gnu #1 SMP 1 x86_64 GNU/Linux

~$ btrfs --version
btrfs-progs v5.6

~$ sudo btrfs balance status /
No balance found on '/'

~$ btrfs fi df /
Data, RAID1: total=446.50GiB, used=446.42GiB
System, RAID1: total=32.00MiB, used=80.00KiB
Metadata, RAID1: total=3.00GiB, used=2.11GiB
GlobalReserve, single: total=512.00MiB, used=5.53MiB

~$ sudo btrfs fi usage /
Overall:
    Device size:                 899.07GiB
    Device allocated:            899.07GiB
    Device unallocated:            2.01MiB
    Device missing:                  0.00B
    Used:                        897.05GiB
    Free (estimated):             85.87MiB      (min: 85.87MiB)
    Data ratio:                       2.00
    Metadata ratio:                   2.00
    Global reserve:              512.00MiB      (used: 5.53MiB)

Data,RAID1: Size:446.50GiB, Used:446.42GiB (99.98%)
   /dev/sda3     446.50GiB
   /dev/sdb3     446.50GiB

Metadata,RAID1: Size:3.00GiB, Used:2.11GiB (70.22%)
   /dev/sda3       3.00GiB
   /dev/sdb3       3.00GiB

System,RAID1: Size:32.00MiB, Used:80.00KiB (0.24%)
   /dev/sda3      32.00MiB
   /dev/sdb3      32.00MiB

Unallocated:
   /dev/sda3       1.00MiB
   /dev/sdb3       1.00MiB

~$ sudo btrfs device stats /
[/dev/sda3].write_io_errs    0
[/dev/sda3].read_io_errs     0
[/dev/sda3].flush_io_errs    0
[/dev/sda3].corruption_errs  0
[/dev/sda3].generation_errs  0
[/dev/sdb3].write_io_errs    0
[/dev/sdb3].read_io_errs     0
[/dev/sdb3].flush_io_errs    0
[/dev/sdb3].corruption_errs  0
[/dev/sdb3].generation_errs  0

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Thank you for any useful hint!
Best regards, Giovanni

-- 
Giovanni Biscuolo

Xelera IT Infrastructures

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