Ubuntu 14.04
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Configure RAID 1
2016/01/27
 
Configure RAID 1 to add 2 new HDDs on a server.
[1] This example is based on the environment below. The new HDD sdb and sdc are newly added on it and configure RAID 1.
root@dlp:~#
df -h

Filesystem                Size  Used Avail Use% Mounted on
udev                      2.0G  4.0K  2.0G   1% /dev
tmpfs                     396M  372K  395M   1% /run
/dev/mapper/tmp--vg-root   26G  1.9G   23G   8% /
none                      4.0K     0  4.0K   0% /sys/fs/cgroup
none                      5.0M     0  5.0M   0% /run/lock
none                      2.0G     0  2.0G   0% /run/shm
none                      100M     0  100M   0% /run/user
/dev/vda1                 236M   97M  127M  44% /boot
[2] Create a partition on new HDD and set RAID flag.
root@dlp:~#
parted --script /dev/sdb "mklabel gpt"

root@dlp:~#
parted --script /dev/sdc "mklabel gpt"

root@dlp:~#
parted --script /dev/sdb "mkpart primary 0% 100%"

root@dlp:~#
parted --script /dev/sdc "mkpart primary 0% 100%"

root@dlp:~#
parted --script /dev/sdb "set 1 raid on"

root@dlp:~#
parted --script /dev/sdc "set 1 raid on"
[3] Configure RAID 1.
# install tools

root@dlp:~#
apt-get -y install mdadm
root@dlp:~#
mdadm --create /dev/md0 --level=raid1 --raid-devices=2 /dev/sdb1 /dev/sdc1

mdadm: Note: this array has metadata at the start and
    may not be suitable as a boot device.  If you plan to
    store '/boot' on this device please ensure that
    your boot-loader understands md/v1.x metadata, or use
    --metadata=0.90
Continue creating array? y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.

# show status

root@dlp:~#
cat /proc/mdstat

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdc1[1] sdb1[0]
      20952960 blocks super 1.2 [2/2] [UU]
      [=====>...............]  resync = 25.0% (5238272/20952960) finish=2.1min speed=119051K/sec

unused devices: <none>

# after few hours later, status turns like follows if syncing finished

root@dlp:~#
cat /proc/mdstat

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdc1[1] sdb1[0]
      20952960 blocks super 1.2 [2/2] [UU]

unused devices: <none>
[4] For example, if a member HDD in RAID array would be failure, re-configure RAID 1 like follows.
# the status is like follows in failure

root@dlp:~#
cat /proc/mdstat

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdc1[1] sdb1[0]
      20952960 blocks super 1.2 [2/1] [U_]

unused devices: <none>

# after swapping new disk, re-configure like follows

root@dlp:~#
mdadm --manage /dev/md0 --add /dev/sdc1

mdadm: added /dev/sdc1
root@dlp:~#
cat /proc/mdstat

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdc1[1] sdb1[0]
      20952960 blocks super 1.2 [2/2] [UU]
      [=====>...............]  resync = 25.0% (5238272/20952960) finish=2.1min speed=119051K/sec

unused devices: <none>
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