Ceph RBD live resize with krbd

The Ubuntu precise 3.8 linux kernel is rebuilt with Laurent Barbe’s patch:

apt-get source linux-image-3.8.0-27-generic
cd linux-lts-raring-3.8.0/
curl https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/patch/?id=d98df63ea7e87d5df4dce0cece0210e2a777ac00 | patch -p1
dpkg-buildpackage -uc -us

and installed with

dpkg -i ../linux-image-3.8.0-27-generic_3.8.0-27.40~precise3_amd64.deb

Live resize of a mounted ext4 file system can then be done as follows:

# rbd create --size 10000 test
# rbd map test
# mkfs.ext4 -q /dev/rbd1
# mount /dev/rbd1 /mnt
# df -h /mnt
Filesystem      Size  Used Avail Use% Mounted on
/dev/rbd1       9.5G   22M  9.0G   1% /mnt
# blockdev --getsize64 /dev/rbd1
10485760000
# rbd resize --size 20000 test
Resizing image: 100% complete...done.
# blockdev --getsize64 /dev/rbd1
20971520000
# resize2fs /dev/rbd1
resize2fs 1.42 (29-Nov-2011)
Filesystem at /dev/rbd1 is mounted on /mnt; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 2
The filesystem on /dev/rbd1 is now 5120000 blocks long.
# df -h /mnt
Filesystem      Size  Used Avail Use% Mounted on
/dev/rbd1        20G   27M   19G   1% /mnt