Repairing the RAID Arrays

After partitioning the disks, you can repair the two logical RAID arrays:

/dev/md0 contains /dev/disk/by-hba-slot/s0p1 and /dev/disk/by-hba-slot/s1p1. It is mounted as /boot.
/dev/md2 contains /dev/disk/by-hba-slot/s0p2 and /dev/disk/by-hba-slot/s1p2. It is mounted as / (root).

Caution:

Do not dismount the /dev/md devices, because that action shuts down the system.

To repair the RAID arrays:

Remove the partitions from the RAID arrays:

# mdadm /dev/md0 -r detached
# mdadm /dev/md2 -r detached

Verify that the RAID arrays are degraded:

# mdadm -Q –-detail /dev/md0
# mdadm -Q –-detail /dev/md2

Verify that the degraded file for each array is set to 1:

# cat /sys/block/md0/md/degraded
1
# cat /sys/block/md2/md/degraded
1

Restore the partitions to the RAID arrays:

# mdadm –-add /dev/md0 /dev/disk/by-hba-slot/snp1
# mdadm –-add /dev/md2 /dev/disk/by-hba-slot/snp2

Check that resynchronization is started, so that /dev/md2 is in a state of recovery and not idle:
```
# cat /sys/block/md2/md/sync_action
repair
```

To verify that resynchronization is proceeding, you can monitor the mdstat file. A counter identifies the percentage complete.

# cat /proc/mdstat

Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[0]
      204736 blocks [2/2] [UU]
 
md2 : active raid1 sdb2[2] sda2[0]
      174079936 blocks [2/1] [U_]
      [============>........]  recovery = 61.6% (107273216/174079936) finish=18.4min speed=60200K/sec

The following output shows that synchronization is complete:

Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[0]
      204736 blocks [2/2] [UU]
 
md2 : active raid1 sdb2[1] sda2[0]
      174079936 blocks [2/2] [UU]
 
unused devices: <none>

Display the content of /etc/mdadm.conf:

# cat /etc/mdadm.conf

# mdadm.conf written out by anaconda
DEVICE partitions
MAILADDR root
ARRAY /dev/md0 level=raid1 num-devices=2 UUID=df1bd885:c1f0f9c2:25d6...
ARRAY /dev/md2 level=raid1 num-devices=2 UUID=6c949a1a:1d45b778:a6da...

Compare the output of the following command with the content of /etc/mdadm.conf from Step 7:
```
# mdadm --examine --brief --scan --config=partitions
```
If the UUIDs in the file are different from UUIDs in the output of the mdadm command:
1. Open /etc/mdadm.conf in a text editor.
2. Select from ARRAY to the end of the file, and delete the selected lines.
3. Copy the output of the command into the file where you deleted the old lines.
4. Save the modified file and exit.
Complete the steps in "Formatting the HDFS Partition of an Operating System Disk".