RAID-1 configuration and management

RAID-1 configuration via Kickstart

(Under construction) How to change the Kickstart file to define RAID-1

The following examples uses two serial ATA disks (/dev/sda and /dev/sdb) with four partitions (/boot, /, swap and /tmp), each in RAID-1 configuration:

part raid.01 --size=128  --ondisk=sda
part raid.02 --size=8192 --ondisk=sda
part raid.03 --size=3072 --ondisk=sda
part raid.04 --size=512 --ondisk=sda

part raid.05 --size=128  --ondisk=sdb
part raid.06 --size=8192 --ondisk=sdb
part raid.07 --size=3072 --ondisk=sdb
part raid.08 --size=512 --ondisk=sdb

raid /boot --level=RAID1 --device=md0 --fstype=ext2 raid.01 raid.05
raid /     --level=RAID1 --device=md1 --fstype=ext3 raid.02 raid.06
raid swap  --level=RAID1 --device=md2 --fstype=swap raid.03 raid.07
raid /tmp  --level=RAID1 --device=md3 --fstype=ext3 raid.04 raid.08

Restoring data on a new disk

OK, so there are two disks in a RAID-1 (mirror) configuration. What to do if on of them dies?

Well, all data are still available on the other disk, so they can be restored when a new disk is placed. The following steps show how to restore the data:

0. Do not reboot the machine! A reboot may change the drive names (e.g., /dev/sdb becoming /dev/sda) and hang the machine if it cannot find the boot loader grub.

1. Remove the partitions of the defect disk from the RAID configuration:

mdadm /dev/mdX -r /dev/sdYZ            (X=0,1,2,... Y=a,b,c,... Z=1,2,3,...)

For example,

mdadm /dev/md0 -r /dev/sdb1

to remove partition 1 on disk sdb from raid device md0.

2. Replace the bad disk by a fresh one. Do not reboot the machine!

3. Rescan the SCSI bus for new devices. Use the script

/usr/local/bin/rescan-sci-bus.sh

(if installed from rpm), or download it from:

http://stal.nikhef.nl/scripts/rescan-scsi-bus.sh

4. Now the partition table should be created on the new disk. Use the following command to clone the partition table of existing disk sdX to the new disk sdY:

sfdisk -d /dev/sdX | \
sed -e s/sdX/sdY/ | \
sdisk /dev/sdY

(using

X=a,b,c,..

and

Y=a,b,c,...

, X different from Y).

5.