To begin with I have to forward you to the Software
RAID HOWTO for background information... Now when you're back I want
to point out that even though the instructions provided below are RedHat
specific (e.g. they depend on kernel support for RAID
# fdisk /dev/sda The number of cylinders for this disk is set to 1106. There is nothing wrong with that, but this is larger than 1024, and could in certain setups cause problems with: 1) software that runs at boot time (e.g., LILO) 2) booting and partitioning software from other OSs (e.g., DOS FDISK, OS/2 FDISK) Command (m for help): p Disk /dev/sda: 255 heads, 63 sectors, 1106 cylinders Units = cylinders of 16065 * 512 bytes
First of all note how large is one cylinder
(Units line above). The catch is that it should be large
enough to accomodate so called RAID persistent block. It takes up to
partition the disk leaving 1 cylinder (or more, enough to accomodate the multi-device superblock mentioned above) gaps(**) between partitions as well as between the last partition and the end of the disk (or extended partition edge(s) for that matter):
Device Boot Start End Blocks Id System /dev/sda1 * 1 131 1052226 83 Linux /dev/sda2 133 165 265072+ 82 Linux swap /dev/sda3 167 1105 7542517+ 83 Linux
# mkinitrd --preload raid1 /boot/initrd-`uname -r`.img `uname -r`
and preload the ramdisk with lilo:
# cat /etc/lilo.conf boot=/dev/sda map=/boot/map install=/boot/boot.b #prompt timeout=50 linear default=linux image=/boot/vmlinuz-2.2.16-3 label=linux initrd=/boot/initrd-2.2.16-3.img read-only root=/dev/sda1 # lilo Added linux *
Needless to mention that compiling customized kernel (beware (*)) with RAID-1 code permanently compiled into it shall do the trick as well. In either case it's more than appropriate to reboot at this point in order to verify that the system is bootable and the raid1.o module is preloded;
# cat /proc/partitions major minor #blocks name 8 0 8886750 sda 8 1 1052226 sda1 8 2 265072 sda2 8 3 7542517 sda3 # mknod /dev/sda b 8 0 # mknod /dev/sda1 b 8 1 # mknod /dev/sda2 b 8 2
Device Boot Start End Blocks Id System /dev/sda1 * 1 132 1060258+ fd Linux raid autodetect /dev/sda2 133 166 273105 fd Linux raid autodetect /dev/sda3 167 1106 7550550 fd Linux raid autodetect Command (m for help): w
# cat /etc/raidtab raiddev /dev/md0 raid-level 1 nr-raid-disks 2 nr-spare-disks 0 chunk-size 4 persistent-superblock 1 device /dev/sda1 raid-disk 0 device /dev/sdp1 failed-disk 1 raiddev /dev/md1 raid-level 1 nr-raid-disks 2 nr-spare-disks 0 chunk-size 4 persistent-superblock 1 device /dev/sda2 raid-disk 0 device /dev/sdp2 failed-disk 1 # grep md\$ /proc/devices 9 md # mknod /dev/md0 b 9 0 mknod: /dev/md0: File exists # mkraid --force /dev/md0 # mknod /dev/md1 b 9 1 # mkraid --force /dev/md1 # cat /proc/mdstat Personalities : [raid1] read_ahead 1024 sectors md0 : active raid1 sda1 1060160 blocks [2/1] [U_] md1 : active raid1 sda2 273024 blocks [2/1] [U_] unused devices: <none>
Well, it's not much of a RAID-1, huh? No, as you see there're no mirrors. Meaningless from first glance but still usefull (well, in my opinion) during installation and especially upgrade when you might choose to detach the old mirror partition and keep it as a "roll-back-quickly" backup.
# mount /dev/md0 /tmp/a # cp -i /etc/raidtab /tmp/a/etc/raidtab.root
# cat /tmp/a/etc/fstab /dev/md0 / ext2 defaults 1 1 /dev/md1 swap swap defaults 0 0 ...
# cat /tmp/a/etc/lilo.conf boot=/dev/md0 map=/boot/map install=/boot/boot.b #prompt timeout=50 linear default=linux image=/boot/vmlinuz-2.2.16-3 label=linux initrd=/boot/initrd-2.2.16-3.img read-only root=/dev/md0 # /tmp/a/sbin/lilo -r /tmp/a boot = /dev/sda, map = /boot/map.0801 Added linux *
# umount /tmp/a # raidstop /dev/md0 # raidstop /dev/md1
# raidhotadd -c /dev/null /dev/md0 /dev/sdb1 # raidhotadd -c /dev/null /dev/md1 /dev/sdb2 # cat /proc/mdstat Personalities : [raid1] read_ahead 1024 sectors md0 : active raid1 sdb1 sda1 1060160 blocks [2/2] [UU] md1 : active raid1 sdb2 sda2 273024 blocks [2/2] [UU] unused devices: <none>
It's definitely good idea to wait till recovery disappers from mdX line before you proceed with mdX+1 if some of the involved partitions reside on the same physical disk. For better performance that is...
Just few words about upgrade procedure. The keyword is "break the mirror before upgrading." Depending on how smart upgrade program is you might also have to change partition system ids to non-raid type as well as fix-up /etc/fstab. If you plan to rebuild some of the file systems you also want to shrink corresponding patition(s) by one cylinder (unless (**) below comes true). I hope you get my drift...
# cat /etc/lilo.conf boot=/dev/sda map=/boot/map install=/boot/boot.b #prompt timeout=50 linear default=linux image=/boot/vmlinuz-2.2.16-3 label=linux initrd=/boot/initrd-2.2.16-3.img read-only root=/dev/sda1 # cat /etc/fstab /dev/md0 / ext2 defaults 1 1 ...
In this case you also want to run lilo twice in order to
disseminate the boot block, e.g.