Giuseppe Scrivano wrote: > Jim Meyering <j...@meyering.net> writes: > >>> Another possible issue with this I can think of is >>> depending on the modification pattern of the COW files, >>> the modification processes could fragment the file or >>> more seriously be given ENOSPC errors. >> I hope btrfs takes care of this behind the scene. >> >> How does the clone work wrt to space consumed, a la df? >> If copying a 1GB file this way does not update usage >> stats to reflect the additional 1GB of space used, ... > > I tried to clone a big file and df reported a different "used blocks" > stat that it was before the clone operation.
How different exactly? OK I tried this myself on F11 with inconclusive results. $ uname -r 2.6.29.6-213.fc11.i586 $ sudo yum install btrfs-progs # dd bs=1M count=300 if=/dev/zero of=/btrfs.img #min size? # mkfs.btrfs /btrfs.img # mkdir /btrfs # mount -o loop /btrfs.img /btrfs # cd /btrfs # dd bs=1M count=100 if=/dev/zero of=alloc.test # df -h . Filesystem Size Used Avail Use% Mounted on /dev/loop0 300M 28K 300M 1% /btrfs # df -h . #only allocated about 30s later Filesystem Size Used Avail Use% Mounted on /dev/loop0 300M 101M 200M 34% /btrfs # /home/padraig/clone_file alloc.test alloc.test.clone # umount /btrfs # mount -o loop /btrfs.img /btrfs # cd btrfs # df -h . Filesystem Size Used Avail Use% Mounted on /dev/loop0 300M 101M 200M 34% /btrfs OK the above suggests that the clone doesn't take any space as I would expect. Then it starts getting confusing... # du -h * 100M alloc.test 244M alloc.test.clone #wha? # dd bs=1M count=200 if=/dev/zero of=use.space dd: writing `use.space': No space left on device 101+0 records in 100+0 records out # ls -l total 454656 -rw-r--r-- 1 root root 104857600 2009-07-28 00:06 alloc.test -rw-r--r-- 1 root root 104857600 2009-07-28 00:07 alloc.test.clone -rw-r--r-- 1 root root 104857600 2009-07-28 00:18 use.space # df -h . Filesystem Size Used Avail Use% Mounted on /dev/loop0 300M 184M 117M 62% /btrfs The above suggests that the clone does actually allocate space but btrfs isn't reporting it through statvfs correctly? If the clone does allocate space, then how can one clone without allocation which could be very useful for snapshotting for example? Also I tried the above twice and both times got: http://www.kerneloops.org/submitresult.php?number=578993 cheers, Pádraig. _______________________________________________ Bug-coreutils mailing list Bug-coreutils@gnu.org http://lists.gnu.org/mailman/listinfo/bug-coreutils
