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HOWTO: Expand a RAID 5 by adding another disk
06/12/09
03:23:24 pm, by richard 
, 1195 words 
Categories: Ubuntu Linux, OS and Systems Administration, Filing Systems, Installation and Configuration
HOWTO: Expand a RAID 5 by adding another disk
You must resize the file system on the new raid system. I use reiserfs so this can be done on the fly while the system is still mounted. If you use ext3 then I believe this has to be done on an unmounted file system. So boot with a rescue disk first.
Now when you check the disk usage with the df command you will see the correct size of the RAID array. The size on my test system has changed from 8Gb to 12Gb, I added a 4Gb disk so this is expected. 4 x 4Gb disks.
Filesystem Size Used Avail Use% Mounted on
/dev/md0 12G 2.9G 9.2G 24% /
Finally you will need to update mdadm.conf with the new drive adding it to the existing list. Too find out all the UUIDs on the system you can use
/dev/sda1: UUID="a0b4a885-6d24-48c8-b7fc-0000395781f9" TYPE="reiserfs"
/dev/sdb1: UUID="89c286e1-79cc-bbfa-d62d-508b2fbf3d7b" TYPE="linux_raid_member"
/dev/sde1: UUID="2796e969-4c73-414f-d62d-508b2fbf3d7b" TYPE="linux_raid_member"
/dev/sdb1: UUID="6282e69d-0ee3-789c-d62d-508b2fbf3d7b" TYPE="linux_raid_member"
/dev/sdc1: UUID="89c286e1-79cc-bbfa-d62d-508b2fbf3d7b" TYPE="linux_raid_member"
Edit /etc/mdadm/mdadm.conf and add the new drive to the ARRAY that of disk you have added the new drive to. Do not just copy my UUIDs they will not be the same as yours 
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Now you need to rebuild the RAM disk image initrd.
Take a look at the man pages for mdadm.conf and update-initramfs.
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