Re: btrfs dev del not transaction protected?

Marc Lehmann
2019-12-20T17:20:50Z

> > Just while I was writing this mail, on 5.4.5, the _newly created_ btrfs
> > filesystem I restored to went into readonly mode with ENOSPC. Another
> > hardware problem?
>
> But mounting with clear_cache,space_cache=v2 didn't help, df still shows 0
> bytes free, "btrfs f us" still shows 3tb unallocated. I'll play around with
> it more...

clear_cache didn't work, but btrfsck --clear-space-cache v1 and .. v2 did
work:

Filesystem Size Used Avail Use% Mounted on
/dev/mapper/xmnt-cold15 27T 23T 3.6T 87% /cold1

Which is rather insane, as I can't see how this filesystem was ever not
mounted without -o space_cache=v2.

Looking at btrfs f u again...

Metadata,single: Size:1.22GiB, Used:0.00B (0.00%)
/dev/mapper/xmnt-cold13 1.22GiB

Metadata,RAID1: Size:27.92GiB, Used:27.90GiB (99.91%)
/dev/mapper/xmnt-cold15 25.46GiB
/dev/mapper/xmnt-cold12 24.46GiB
/dev/mapper/xmnt-cold13 5.92GiB

System,RAID1: Size:32.00MiB, Used:2.16MiB (6.74%)
/dev/mapper/xmnt-cold15 32.00MiB
/dev/mapper/xmnt-cold12 32.00MiB

Unallocated:
/dev/mapper/xmnt-cold15 1.00MiB
/dev/mapper/xmnt-cold12 1.00MiB
/dev/mapper/xmnt-cold13 3.24TiB

Did this happen because metadata is raid1 and two of the disks were full,
and for some reason, btrfsck freed up a tiny bit of space somewhere?