How to mount software RAID1

Hello,

We move now one hdd from old server and want to mount.
Disk:

root@team-G41MT-S2PT:~# fdisk -l /dev/sdb
Disk /dev/sdb: 698,7 GiB, 750156374016 bytes, 1465149168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device Boot Start End Sectors Size Id Type
/dev/sdb1 63 1465144064 1465144002 698,7G fd Linux raid autodetect

Examine the patition:

root@team-G41MT-S2PT:~# mdadm –examine /dev/sdb1
/dev/sdb1:
Magic : a92b4efc
Version : 0.90.00
UUID : 0d198050:1986aa3b:4c47847c:235cc6f1
Creation Time : Wed Dec 8 11:01:14 2010
Raid Level : raid1
Used Dev Size : 732571904 (698.64 GiB 750.15 GB)
Array Size : 732571904 (698.64 GiB 750.15 GB)
Raid Devices : 2
Total Devices : 1
Preferred Minor : 9

Update Time : Wed Jan 25 16:11:22 2017
State : clean
Active Devices : 1
Working Devices : 1
Failed Devices : 1
Spare Devices : 0
Checksum : 10a1f0fa – correct
Events : 886
Number Major Minor RaidDevice State
this 0 8 17 0 active sync /dev/sdb1

0 0 8 17 0 active sync /dev/sdb1
1 1 0 0 1 faulty removed

I needed to create md virtual device using mdadm:

root@team-G41MT-S2PT:~# mdadm -A -R /dev/md56 /dev/sdb1

So now it could be mounted:

root@team-G41MT-S2PT:~# mount /dev/md56 /mnt/disk/

If you want to removed md virtual device you have to unmount raid device and stop.

root@team-G41MT-S2PT:~# umount /mnt/disk
root@team-G41MT-S2PT:~# mdadm -S /dev/md56
mdadm: stopped /dev/md56

How to fix auto-read-only mdadm.

This guide shows you a simple way to fix your mdadm raid based drives which are not syncing or in the auto-read-only mode.

To find the names of your drives which are under auto-read-only mode or not syncing

cat /proc/mdstat

Force the drives to sync.

mdadm --readwrite /dev/md9

Replace md9 with the name of the drive like md127 etc.
server ~ # cat /proc/mdstat
Personalities : [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] [linear] [multipath]
md125 : active (auto-read-only) raid1 sda1[0] sdb1[1]
      192640 blocks [2/2] [UU]

md126 : active raid1 sda5[0] sdb5[1]
      97650944 blocks [2/2] [UU]
        resync=DELAYED

md127 : active raid1 sdb2[1] sda2[0]
      97659008 blocks [2/2] [UU]
      [=>...................]  resync =  8.8% (8686848/97659008) finish=64.0min speed=23148K/sec

md128 : active (auto-read-only) raid1 sdb6[1] sda6[0]
      288875200 blocks [2/2] [UU]

Source Info: http://wiki.crowncloud.net/doku.php/how_to_fix_auto-read-only_mdadm