Whilst I use LVM without RAID to manage the drives on my media server, because the media rarely changes so the offline backup is easy to keep in sync, I have started using RAID 1 to mirror the contents of my file server to guard against the failure of a single drive. This is because the data changes sufficiently often on the file server that my regular backup might get out of sync by up to a day which could lose me a days work.
- Using the Debian alternate install CD, at the partion disks screen, select manual
- Select the free space on your first drive and create 3 new partitions as follows: 2GB for /boot, 2GB for SWAP, Remainder for /
- Select "physical volume for RAID" at this point and ensure that the boot partition is marked as bootable.
- Repeat the above steps for the second drive
- Now select "Configure software RAID" from the main partition disks screen
- Create 3 Multidisk (MD) devices with each configured as RAID 1 with 2 active and 0 hotspace disks, one MD device for each of the boot swap and root partitions. Select the correct corresponding matched partitions to include in each MD device, e.g. sda1 and sdb1, sda2 and sdb2, sda3 and sdb3
- After returning once more to the main Partition Disks screen you should see the RAID devices that you just created listed alongside the partitions from before. Create file systems on each RAID device in the same fashion as for normal, non-RAID, partitions, e.g. RAID device #0: type ext3 mounted at /boot, RAID device #1: type SWAP, RAID device #2: type ext3 mounted at /
- Write the changes to disk and continue with a normal installation
After installation you must also install grub to the master boot record on the second drive in the RAID array so that the system can boot from the other drive in the case of one drive failing.
$ sudo grub-install /dev/sda
$ sudo grub
grub> device (hd0) /dev/sdb
grub> root (hd0,0)
grub> setup (hd0)
grub> quit
Verify that you have the correct filesystems in the correct places, e.g.
$ grep /dev/md /etc/fstab
$ df -h /
The status of RAID devices can be checked using the /proc/mdstat file. Each mdN device contains two sdXN disks and each mdN device should have "2/2" and "UU":
$ cat /proc/mdstat
The mdadm utility gives more details:
$ sudo mdadm --query --detail /dev/md0
