I don't quite understand the behavior of "btrfs fi defrag"
~# truncate -s2G ~/a
~# mkfs.btrfs ~/a
nodesize 4096 leafsize 4096 sectorsize 4096 size 2.00GB
~# mount -o loop ~/a /mnt/1
/mnt/1# cd x
/mnt/1# df -h .
Filesystem Size Used Avail Use% Mounted on
/dev/loop1 2.0G 64K 1.8G 1% /mnt/1
/mnt/1# yes | head -c400M > a
/mnt/1# df -h .
Filesystem Size Used Avail Use% Mounted on
/dev/loop1 2.0G 64K 1.8G 1% /mnt/1
/mnt/1# sync
/mnt/1# df -h .
Filesystem Size Used Avail Use% Mounted on
/dev/loop1 2.0G 402M 1.4G 23% /mnt/1
/mnt/1# btrfs fi defrag -c a
(exit status == 20 BTW).
(20)/mnt/1# sync
/mnt/1# df -h .
Filesystem Size Used Avail Use% Mounted on
/dev/loop1 2.0G 415M 994M 30% /mnt/1
No space gain, even lost 15M or 400M depending on how you look at it.
/mnt/1# btrfs fi defrag a
(20)/mnt/1# sync
/mnt/1# df -h .
Filesystem Size Used Avail Use% Mounted on
/dev/loop1 2.0G 797M 612M 57% /mnt/1
Lost another 400M.
/mnt/1# ls -l
total 409600
-rw-r--r-- 1 root root 419430400 Oct 27 19:53 a
/mnt/1# btrfs fi balance .
/mnt/1# sync
/mnt/1# df -h .
Filesystem Size Used Avail Use% Mounted on
/dev/loop1 2.0G 798M 845M 49% /mnt/1
Possibly reclaimed some of the space?
At the point where it says 612M free, if I do:
/mnt/1# cat < /dev/zero > b
cat: write error: No space left on device
/mnt/1# ls -lh b
-rw-r--r-- 1 root root 612M Oct 27 20:14 b
There was indeed 612M free.
When the FS is mounted with compress:
~# mkfs.btrfs ./a
nodesize 4096 leafsize 4096 sectorsize 4096 size 2.00GB
~# mount -o compress ./a /mnt/1
~# cd /mnt/1
/mnt/1# yes | head -c400M > a
/mnt/1# sync
/mnt/1# df -h .
Filesystem Size Used Avail Use% Mounted on
/dev/loop1 2.0G 14M 1.8G 1% /mnt/1
/mnt/1# btrfs fi defrag -c ./a
(20)/mnt/1# sync
/mnt/1# df -h .
Filesystem Size Used Avail Use% Mounted on
/dev/loop1 2.0G 21M 1.4G 2% /mnt/1
Lost 400M?
/mnt/1# btrfs fi defrag ./a
(20)/mnt/1# sync
/mnt/1# df -h .
Filesystem Size Used Avail Use% Mounted on
/dev/loop1 2.0G 21M 1.4G 2% /mnt/1
I take it it doesn't uncompress?
I'm a bit confused here.
(that's with 3.0 amd64)
--
Stephane
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