3.2 Growing A Degraded Array

Before we boot into the rescue system, we must make sure that /dev/sda5 is really removed from the array:

mdadm --manage /dev/md1 --fail /dev/sda5
mdadm --manage /dev/md1 --remove /dev/sda5

Then we overwrite the superblock on /dev/sda5 (this is very important - if you forget this, the system might now boot anymore after the resizal!):

mdadm --zero-superblock /dev/sda5

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

...and start LVM:

/etc/init.d/lvm start

Now we can grow /dev/md1 as follows:

mdadm --grow /dev/md1 --size=max

--size=max means the largest possible value. You can as well specify a size in KiBytes (see previous chapter).

Then we grow the PV to the largest possible value...

pvresize /dev/md1

... and take a look at

vgdisplay

root@Knoppix:~# vgdisplay
  --- Volume group ---
  VG Name               server1
  System ID
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  29
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                2
  Open LV               0
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               4.75 GB
  PE Size               4.00 MB
  Total PE              1217
  Alloc PE / Size       1023 / 4.00 GB
  Free  PE / Size       194 / 776.00 MB
  VG UUID               X3ZYTy-39yq-20k7-GCGk-vKVU-Xe0i-REdEu0

root@Knoppix:~#

We have 194 free PE that we can allocate to our /dev/server1/root LV:

lvextend -l +194 /dev/server1/root

Then we run a file system check...

e2fsck -f /dev/server1/root

..., resize the file system...

resize2fs /dev/server1/root

... and check the file system again:

e2fsck -f /dev/server1/root

Then boot into the normal system again and run the following two commands to add /dev/sda5 back to the array /dev/md1:

mdadm --zero-superblock /dev/sda5
mdadm -a /dev/md1 /dev/sda5

Take a look at

cat /proc/mdstat

and you should see that /dev/sdb5 and /dev/sda5 are now being synced.

4 Links

• Knoppix: http://www.knoppix.net/