My work around above (described in the section "code working around the issue")
does not consistently work. I was probably just lucky a few times in a row.
I tried several times, with varying delays between creating the huge file and
transferring the snapshot but most of them fail and there seem to be no
correlation with the delay.
Actually, the same problem arises using rsync so it must not be
restricted to btrfs send/receive.
$ rsync -a --stats --one-file-system /mnt/btr_root_pool/@.20170212T1133/
/mnt/btr_root_bac/
rsync: rename
"/mnt/btr_root_bac/lib/modules/4.8.0-22-generic/kernel/drivers/staging/comedi/drivers/.fl512.ko.2UT9JI"
->
"lib/modules/4.8.0-22-generic/kernel/drivers/staging/comedi/drivers/fl512.ko":
No space left on device (28)
Assuming that there may be a problem with btrfs not being able to grow the file
system fast enough, I have also tried to limit the transfer rate by using pv:
for RATE in $(seq 2 2 40 | shuf); do
echo -e "\n\n\n=================\n\nRATE=${RATE}"
mountpoint -q /mnt/btr_root_bac && umount /mnt/btr_root_bac
dd if=/dev/zero of=/dev/sda5 bs=8M count=10
mkfs.btrfs /dev/sda5
mount -o subvolid=0 /dev/sda5 /mnt/btr_root_bac
btrfs fi df /mnt/btr_root_bac/
btrfs send /mnt/btr_root_pool/@.20170212T1133/ | pv --rate-limit ${RATE}m |
btrfs receive -vvvv /mnt/btr_root_bac/ 2>&1 | grep -e ERROR -e RECEIVED
btrfs fi df /mnt/btr_root_bac/
done
The results seem to suggest that the disk operations have a higher chance of
suceeding with slower transfer rates:
RATE=2 RECEIVED
RATE=4 RECEIVED
RATE=6 RECEIVED
RATE=8 RECEIVED
RATE=10 RECEIVED
RATE=12 RECEIVED
RATE=14 ERROR
RATE=16 ERROR
RATE=18 ERROR
RATE=20 ERROR
RATE=22 ERROR
RATE=24 ERROR
RATE=26 RECEIVED
RATE=28 ERROR
RATE=30 ERROR
RATE=32 RECEIVED
RATE=34 ERROR
RATE=36 ERROR
RATE=38 ERROR
RATE=40 ERROR
Mounting /dev/sda5 with enospc_debug does not seem to add any useful
information to /var/log/syslog.
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https://bugs.launchpad.net/bugs/1664013
Title:
"btrfs receive" throws "No space left on device" on empty and large
enough fs
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