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How to install Software Raid
Software Raid1 (Mirroring)をインストール時に構築しても、ブートローダ(grub)はディスク１には書き込まれるけど、ディスク２には書き込まれない。(ブートローダはMBR = master boot record に書き込まれる)
この状態だと、ディスク１にトラブルがあった時、ディスク２のみでの起動は不可能。
そこで、ディスク２に手動でgrubをインストール。
1, Check /boot directory
# df
then you know where /boot is located. (whether /boot is included in / directory or not.)
In almost cases, /boot is /dev/md0
2, Check which physical disk consists of /dev/md0
# cat /proc/mdstat
then you know /dev/md0 consists of /dev/sda1 and /dev/sdb1
/dev/sda1 is disk1.
/dev/sdb1 is disk2.
3, setup grub
# grub
> device (hd0) /dev/sdb
> root (hd0,0)
> install /grub/stage1 (hd0) /grub/stage2 p /grub/grub.conf
> quit
4, Check /ect/raidtab
Raid does not work well without this file.
If nothing in the system, create manually.
raiddev /dev/md0
raid-level 1
nr-raid-disks 2
chunk-size 256
persistent-superblock 1
nr-spare-disks 0
device /dev/sda1
raid-disk 0
device /dev/sdb1
raid-disk 1
and mention all md* like above.
Synchronize disk1 and 2
# raidhotadd /dev/md0 /dev/sdb1
Synchronize sdb1 to sda1
or (It depends on Linux distribution and version.)
# mdadm --add /dev/md0 /dev/sdb1
Run for all drive which wants to synchronize.
Check raid status
# cat /proc/mdstat
# cat /etc/raidtab
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reference
http://www.miraclelinux.com/technet/faq/data/00080.html