3 Degraded Array
I will describe how to resize the degraded array /dev/md2, made up of /dev/sda3 and /dev/sdb3, where /dev/sda3 has failed:
server1:~# cat /proc/mdstat
Personalities : [raid1]
md2 : active raid1 sdb3[1]
4594496 blocks [2/1] [_U]
md1 : active raid1 sda2[0] sdb2[1]
497920 blocks [2/2] [UU]
md0 : active raid1 sda1[0] sdb1[1]
144448 blocks [2/2] [UU]
unused devices: <none>
server1:~#
3.1 Shrinking A Degraded Array
Before we boot into the rescue system, we must make sure that /dev/sda3 is really removed from the array:
mdadm --manage /dev/md2 --fail /dev/sda3
mdadm --manage /dev/md2 --remove /dev/sda3
Then we overwrite the superblock on /dev/sda3 (this is very important - if you forget this, the system might now boot anymore after the resizal!):
mdadm --zero-superblock /dev/sda3
Boot into your rescue system and activate all needed modules:
modprobe md
modprobe linear
modprobe multipath
modprobe raid0
modprobe raid1
modprobe raid5
modprobe raid6
modprobe raid10
Then activate your RAID arrays:
cp /etc/mdadm/mdadm.conf /etc/mdadm/mdadm.conf_orig
mdadm --examine --scan >> /etc/mdadm/mdadm.conf
mdadm -A --scan
Run
e2fsck -f /dev/md2
to check the file system.
/dev/md2 has a size of 40GB; I want to shrink it to 30GB. First we have to shrink the file system with resize2fs; to make sure that the file system fits into the 30GB, we make it a little bit smaller (25GB) so we have a little security margin, shrink /dev/md2 to 30GB, and the resize the file system (again with resize2fs) to the max. possible value:
resize2fs /dev/md2 25G
Now we shrink /dev/md2 to 30GB. The --size value must be in KiBytes (30 x 1024 x 1024 = 31457280); make sure it can be divided by 64:
mdadm --grow /dev/md2 --size=31457280
Next we grow the file system to the largest possible value (if you don't specify a size, resize2fs will use the largest possible value)...
resize2fs /dev/md2
... and run a file system check again:
e2fsck -f /dev/md2
Then boot into the normal system again and run the following two commands to add /dev/sda3 back to the array /dev/md2:
mdadm --zero-superblock /dev/sda3
mdadm -a /dev/md2 /dev/sda3
Take a look at
cat /proc/mdstat
and you should see that /dev/sdb3 and /dev/sda3 are now being synced.
3.2 Growing A Degraded Array
Before we boot into the rescue system, we must make sure that /dev/sda3 is really removed from the array:
mdadm --manage /dev/md2 --fail /dev/sda3
mdadm --manage /dev/md2 --remove /dev/sda3
Then we overwrite the superblock on /dev/sda3 (this is very important - if you forget this, the system might now boot anymore after the resizal!):
mdadm --zero-superblock /dev/sda3
Boot into your rescue system and activate all needed modules:
modprobe md
modprobe linear
modprobe multipath
modprobe raid0
modprobe raid1
modprobe raid5
modprobe raid6
modprobe raid10
Then activate your RAID arrays:
cp /etc/mdadm/mdadm.conf /etc/mdadm/mdadm.conf_orig
mdadm --examine --scan >> /etc/mdadm/mdadm.conf
mdadm -A --scan
Now we can grow /dev/md2 as follows:
mdadm --grow /dev/md2 --size=max
--size=max means the largest possible value. You can as well specify a size in KiBytes (see previous chapter).
Then we run a file system check...
e2fsck -f /dev/md2
..., resize the file system...
resize2fs /dev/md2
... and check the file system again:
e2fsck -f /dev/md2
Then boot into the normal system again and run the following two commands to add /dev/sda3 back to the array /dev/md2:
mdadm --zero-superblock /dev/sda3
mdadm -a /dev/md2 /dev/sda3
Take a look at
cat /proc/mdstat
and you should see that /dev/sdb3 and /dev/sda3 are now being synced.
4 Links
- Knoppix: http://www.knoppix.net/