why am I getting "No space left on device" here?

Tomasz Chmielewski
2014-01-15T11:02:12Z

I'm no longer able to write to this btrfs filesystem:

# df -h /home
Filesystem Size Used Avail Use% Mounted on
/dev/sdb4 5.2T 3.6T 1.6T 71% /home

# btrfs fi show /home
Label: crawler-btrfs uuid: 60f1759c-45f6-4484-9f60-66a4e9bbf2b6
Total devices 2 FS bytes used 1.80TiB
devid 3 size 2.56TiB used 1.80TiB path /dev/sdb4
devid 4 size 2.56TiB used 1.80TiB path /dev/sda4

Btrfs v3.12

# btrfs filesystem df /home
Data, RAID1: total=1.75TiB, used=1.75TiB
System, RAID1: total=32.00MiB, used=268.00KiB
Metadata, RAID1: total=53.00GiB, used=51.71GiB

However:

# dd if=/dev/urandom of=bigfile
dd: writing to `bigfile': No space left on device
186+0 records in
185+0 records out
94720 bytes (95 kB) copied, 0.0144045 s, 6.6 MB/s

I don't understand why - can anyone explain?

--
Tomasz Chmielewski