Working with software RAID

see also:

• Gentoo Howto on RAID
• growing ext3 partition on RAID1 without rebooting
• LVM

Good article (based on the one that has already been available on old TNT site) on this topic is on URL: http://www.rot13.org/~dpavlin/md-raid1.html

TODO

Creating a new one

 mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sda1 /dev/sdb1 /dev/sdc1

Adding spare to RAID5

 mdadm --add /dev/md0 /dev/sdh1

Fixing /etc/mdadm/mdadm.conf

 echo "DEVICE partitions" > /etc/mdadm/mdadm.conf
 mdadm --detail --scan >> /etc/mdadm/mdadm.conf

Copying the partition table from working HDD to new one

 sfdisk -d /dev/sda > /tmp/partions
 sfdisk --force /dev/sdb < /tmp/partions 

Adding partitions back to raid

 mdadm --add /dev/md0 /dev/sdb1
 mdadm --add /dev/md1 /dev/sdb2
 mdadm --add /dev/md2 /dev/sdb3
 mdadm --add /dev/md3 /dev/sdb4

How to know which disk to remove?

The safest way (IMHO) to know which disk to remove is to write down the serial number of the disk, e.g. using smartctl, and then check the back side of each disk for the matching serial number.

 smartctl -i /dev/hda | grep Serial
 smartctl -i /dev/hde | grep Serial
 smartctl -i /dev/hdg | grep Serial

Force your md array to recheck parity from time to time, to assure data consistency. The following command will read every block on every disk in the md0 array:

 echo check > /sys/block/md0/md/sync_action

 md0 : active (auto-read-only) raid1 sda1[0] sdb1[1]
       1951744 blocks [2/2] [UU]

to fix:

 # mdadm --readwrite /dev/md0

 blockdev --rereadpt /dev/device

see also: Very detailed instalation of fedora4, GRUB Splash Image Howto

 [root@fedora4 ~]# grub
 
     GNU GRUB  version 0.95  (640K lower / 3072K upper memory)
 
  [ Minimal BASH-like line editing is supported.  For the first word, TAB 
    lists possible command completions.  Anywhere else TAB lists the possible
    completions of a device/filename.]

 grub> root (hd0,0)
  Filesystem type is ext2fs, partition type 0xfd
 
 grub> setup (hd0)
  Checking if "/boot/grub/stage1" exists... yes
  Checking if "/boot/grub/stage2" exists... yes
  Checking if "/boot/grub/e2fs_stage1_5" exists... yes
  Running "embed /boot/grub/e2fs_stage1_5 (hd0)"...  15 sectors are embedded.
 succeeded
  Running "install /boot/grub/stage1 (hd0) (hd0)1+15 p (hd0,0)/boot/grub/stage2
 /boot/grub/grub.conf"... succeeded
 Done.
 
 grub> root (hd1,0)
  Filesystem type is ext2fs, partition type 0xfd
 
 grub> setup (hd1)
  Checking if "/boot/grub/stage1" exists... yes
  Checking if "/boot/grub/stage2" exists... yes
  Checking if "/boot/grub/e2fs_stage1_5" exists... yes
  Running "embed /boot/grub/e2fs_stage1_5 (hd1)"...  15 sectors are embedded.
 succeeded
 Running "install /boot/grub/stage1 (hd1) (hd1)1+15 p (hd1,0)/boot/grub/stage2
 /boot/grub/grub.conf"... succeeded
Done.
 
grub> quit