Re: ENOSPC on mostly empty file system

["Holger Hoffstätte" <holger.hoffstaette@googlemail.com>]

On Tue, 09 Sep 2014 23:49:10 +0200, Arnd Bergmann wrote:

> Label: none  uuid: 1d88cccb-3d0e-42d9-8252-a226dc5c2e47
>         Total devices 1 FS bytes used 8.79GB
>         devid    1 size 67.14GB used 67.14GB path /dev/sdc6
                          ^^^^^^^^^^^^^^^^^^^^ *ding ding ding*

The term "used" is confusing here and really should be called
"allocated", since it's more than the number of actually used
bytes. Note that df shows that you "have" ~66GB data and ~1GB
metadata (giving approx. ~67GB), despite the fact that of those
65GB data allocated only ~8GB are actually used.

However all these reserved data chunks are preventing the metadata
space from expanding, which is pretty full:
Metadata, DUP: total=1.00GB, used=799.54MB

Here "total" also should be "allocated/reserved" and is 1GB, but
btrfs feels it's necessary to allocate a new metadata chunk
(which would also increase "total") and fails.

Running balance with -dusage=x will garbage-collect the reserved but
mostly-empty data chunks with "up to x" percent actual usage.

-h