Btrfs Online Resizing

http://kerneltrap.org/Linux/Btrfs_Online_Resizing_Ext3_Conversion_and_More

[ Resizing ]

In order to demonstrate and test the back references, I've added an online
resizer, which can both grow and shrink the filesystem:

mount -t btrfs /dev/xxx /mnt

# add 2GB to the FS
btrfsctl -r +2g /mnt

# shrink the FS by 4GB
btrfsctl -r -4g /mnt

# Explicitly set the FS size
btrfsctl -r 20g /mnt

# Use 'max' to grow the FS to the limit of the device
btrfsctl -r max /mnt