drewster
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Just built a new server running a simple software RAID1 setup on Ubuntu.
I documented the process on rebuilding the array when replacing one of the drives. I couldn't find very good current documentation on this, so maybe this will help some of you if you ever need to replace a faulty drive on a newer linux system.
On the setup below I have two RAID arrays setup, one for the main root file-system, and one for the swap drive. (md0, and md1)
To Determine if RAID is healthy
cat /proc/mdstat
Should look like this:
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md1 : active raid1 sdb5[1] sda5[0]
12209280 blocks [2/2] [UU]
md0 : active raid1 sdb1[1] sda1[0]
231986496 blocks [2/2] [UU]
The hard drive is split into two RAID partitions. md0 is the main file-system, and md1 is the swap file.
If either partition show [UU] then things are healthy, if it shows [_U] then one of the drives is not working properly in the RAID array.
You will notice md1 shows usage of sdb5 and sda5, md0 uses sdb1 and sda1. sda and sdb are the two physical drives in the machine. If you do not see any sda or sdb partitions when you run cat /proc/mdstat that means that drive is not currently being utilized in the array.
The partition tables for sda and sdb have been previously saved to /raidinfo/partitions.sda and /raidinfo/partitions.sdb using the command:
sfdisk -d /dev/sda > /raidinfo/partitions.sda
sfdisk -d /dev/sdb > /raidinfo/partitions.sdb
If one of the drives were to be replaced, the steps to rebuild the array are as follows:
1. Determine which drive is not showing up on cat /proc/mdstat (sda or sdb)
2. Repartition the new drive using the backed up partition table
sfdisk /dev/sda < /raidinfo/partitions.sda (if the sda drive failed)
sfdisk /dev/sdb < /raidinfo/partitions.sdb (if the sdb drive failed)
3. Add the drive back into the array
mdadm -add /dev/md0 /dev/sda1 (if the sda is the new drive)
or
mdadm -add /dev/md0 /dev/sdb1 (if the sdb is the new drive)
then
mdadm --add /dev/md1 /dev/sda5 (if the sda is the new drive)
or
mdadm --add /dev/md1 /dev/sdb5 (if the sdb is the new drive)
This step may take several hours to rebuild. You can check the progress of the rebuild by running this command again:
cat /proc/mdstat
Once the RAID array has been rebuilt, you will need to rewrite the MBR (Master boot record) to both drives. This will allow you to boot off of either drive if one of them fails again in the future. Type the following commands:
grub
device (hd0) /dev/sda
root (hd0,0)
setup (hd0)
device (hd1) /dev/sdb
root (hd1,0)
setup (hd1)
quit
Finally, reboot and check cat /proc/mdstat to make sure things look healthy again.
I documented the process on rebuilding the array when replacing one of the drives. I couldn't find very good current documentation on this, so maybe this will help some of you if you ever need to replace a faulty drive on a newer linux system.
On the setup below I have two RAID arrays setup, one for the main root file-system, and one for the swap drive. (md0, and md1)
To Determine if RAID is healthy
cat /proc/mdstat
Should look like this:
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md1 : active raid1 sdb5[1] sda5[0]
12209280 blocks [2/2] [UU]
md0 : active raid1 sdb1[1] sda1[0]
231986496 blocks [2/2] [UU]
The hard drive is split into two RAID partitions. md0 is the main file-system, and md1 is the swap file.
If either partition show [UU] then things are healthy, if it shows [_U] then one of the drives is not working properly in the RAID array.
You will notice md1 shows usage of sdb5 and sda5, md0 uses sdb1 and sda1. sda and sdb are the two physical drives in the machine. If you do not see any sda or sdb partitions when you run cat /proc/mdstat that means that drive is not currently being utilized in the array.
The partition tables for sda and sdb have been previously saved to /raidinfo/partitions.sda and /raidinfo/partitions.sdb using the command:
sfdisk -d /dev/sda > /raidinfo/partitions.sda
sfdisk -d /dev/sdb > /raidinfo/partitions.sdb
If one of the drives were to be replaced, the steps to rebuild the array are as follows:
1. Determine which drive is not showing up on cat /proc/mdstat (sda or sdb)
2. Repartition the new drive using the backed up partition table
sfdisk /dev/sda < /raidinfo/partitions.sda (if the sda drive failed)
sfdisk /dev/sdb < /raidinfo/partitions.sdb (if the sdb drive failed)
3. Add the drive back into the array
mdadm -add /dev/md0 /dev/sda1 (if the sda is the new drive)
or
mdadm -add /dev/md0 /dev/sdb1 (if the sdb is the new drive)
then
mdadm --add /dev/md1 /dev/sda5 (if the sda is the new drive)
or
mdadm --add /dev/md1 /dev/sdb5 (if the sdb is the new drive)
This step may take several hours to rebuild. You can check the progress of the rebuild by running this command again:
cat /proc/mdstat
Once the RAID array has been rebuilt, you will need to rewrite the MBR (Master boot record) to both drives. This will allow you to boot off of either drive if one of them fails again in the future. Type the following commands:
grub
device (hd0) /dev/sda
root (hd0,0)
setup (hd0)
device (hd1) /dev/sdb
root (hd1,0)
setup (hd1)
quit
Finally, reboot and check cat /proc/mdstat to make sure things look healthy again.
Last edited:
