Fajar A. Nugraha wrote: > On Wed, Dec 28, 2011 at 11:57 PM, Martin Steigerwald > <Martin@xxxxxxxxxxxx> wrote: >> But BTRFS does not: >> >> merkaba:~> fstrim -v / >> /: 4431613952 bytes were trimmed >> merkaba:~> fstrim -v / >> /: 4341846016 bytes were trimmed > > .... and apparently it can't trim everything. Or maybe my kernel is > just too old. > > > $ sudo fstrim -v / > 2258165760 Bytes was trimmed > > $ df -h / > Filesystem Size Used Avail Use% Mounted on > /dev/sda6 50G 34G 12G 75% / > > $ mount | grep "/ " > /dev/sda6 on / type btrfs (rw,noatime,subvolid=258,compress-force=lzo) > > so only about 2G out of 12G can be trimmed. This is on kernel 3.1.4. > That's because only free spaces in block groups will be trimmed. Btrfs allocates space from block groups, and when there's no space availabe, it will allocate a new block group from the pool. In your case there's ~10G in the pool. You can do a "btrfs fi df /", and you'll see the total size of existing block groups. You can empty the pool by: # dd if=/dev/zero of=/mytmpfile bs=1M Then release the space (but it won't return back to the pool): # rm /mytmpfile # sync and try "btrfs fi df /" and trim again. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
