I've been trying to run PostgreSQL with a ~20-30 GB database on a btrfs
filesystem (rest of the filesystem filled with KVM images, compressed
archives etc.). Snapshots are cool, and let you rollback to a different
database version easily ;)
Unfortunately, running PostgreSQL on btrfs wasn't very reliable as I was
getting rather frequent "No space left" for some disk intensive
operations (CREATE INDEX, REINDEX, VACUUM ANALYZE).
As the error happens, I still have around 80 GB free space on the
filesystem:
Filesystem Size Used Avail Use% Mounted on
/dev/sdb4 336G 255G 80G 77% /mnt/btrfs
What's even more interesting, after the error happened, I'm able to
write a ~85 GB file with dd before it exits with "out of space" (with
and without the oflag=direct):
# dd if=/dev/urandom of=bigfile bs=1M
dd: writing `bigfile': No space left on device
81056+0 records in
81055+0 records out
84992327680 bytes (85 GB) copied, 9429.28 s, 9.0 MB/s
The kernel used was 2.6.39-rc5.
If it matters, I had the filesystem mounted with compress-force flag:
/dev/sdb4 on /mnt/btrfs type btrfs (rw,noatime,compress-force)
--
Tomasz Chmielewski
http://wpkg.org
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