Craigje: Created page with "= Rebuilding and Creating RAID 1 Arrays with mdadm = == Crating Arrays == To create a mirrored array with two drives, `sda` and `sdb`, on partitions, <..."

2019-06-03T14:11:48Z

Created page with "= Rebuilding and Creating RAID 1 Arrays with mdadm = == Crating Arrays == To create a mirrored array with two drives, <code>sda</code> and <code>sdb</code>, on partitions, <..."

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= Rebuilding and Creating RAID 1 Arrays with mdadm =

== Crating Arrays ==

To create a mirrored array with two drives, <code>sda</code> and <code>sdb</code>, on partitions, <code>sda1</code> and <code>sdb1</code>:

<pre class="text">mdadm --create --verbose /dev/md0 --level=raid1 --raid-devices=2 /dev/sda1 /dev/sdb1
</pre>
Now you can monitor the status of the building of the array with:

<pre class="text">cat /proc/mdstat
</pre>
Once finished, save your <code>mdadm</code> configuration with:

<pre class="text">mdadm --verbose --detail --scan > /etc/mdadm.conf
</pre>
You may need to edit this file to remove unwanted lines or to add an email address to <code>MAILADDR</code> to be notified if a drive failure occurs:

<pre class="text">MAILADDR user1@dom1.com, user2@dom2.com
</pre>
On some systems, <code>mdadm</code>'s configuration file is <code>/etc/mdadm/mdadm.conf</code>, it is very important to put the configuration in the correct location.

== Rebuilding Arrays ==

If a drive ever fails, or is the system is booted with a drive removed, you will need to add it back into the array.

=== Failed Drive ===

In this example, <code>/dev/sda1</code> and <code>/dev/sdb1</code> make up the RAID 1 array <code>/dev/md0</code>. Let us say that <code>/dev/sdb</code> fails.

==== Determining failed drive ====

Run

<pre class="text">cat /proc/mdstat
</pre>
<pre class="text">[root@lo4 ~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdb1[1](F) sda1[0]
204736 blocks super 1.0 [2/1] [U_]

unused devices: <none>
</pre>
When a drive fails or is missing, you will see an underscore in the array output (<code>[U_]</code> instead of <code>[UU]</code>). <code>(F)</code> will be displayed next to the failed drive (<code>sdb1[1](F)</code>).<br /> If not, running <code>lsblk</code> or <code>fdisk -l</code> may help you determine which drive it is that failed

<pre class="text">hdparm -I /dev/sda | grep "Serial Number"
</pre>
Will give you the serial number of <code>/dev/sda</code>, which may help you identify physical disks as well.

==== Remove Failed Drive ====

If a drive has has failed, it should be removed from the <code>mdadm</code> array before being replaced.

<pre class="text">mdadm --manage /dev/md0 --fail /dev/sdb1
</pre>
<pre class="text">[root@lo4 ~]# mdadm --manage /dev/md0 --fail /dev/sdb1
mdadm: set /dev/sdb1 faulty in /dev/md0
</pre>
Now, we can remove it from the array.

<pre class="text">mdadm --manage /dev/md0 --remove /dev/sdb1
</pre>
<pre class="text">[root@lo4 ~]# mdadm --manage /dev/md0 --remove /dev/sdb1
mdadm: hot removed /dev/sdb1 from /dev/md0
</pre>
Check <code>/proc/mdstat</code>. There should no longer be any <code>(F)</code> or listed drive besides <code>sda1[0]</code>.

Power down the system.

<pre class="text">shutdown -h now
</pre>
==== Replace Drive ====

Now that everything is powered down, remove the failed HDD then replace it with the new one.

Once the drive is replaced, boot the system back up.

==== Add New Drive to Array ====

Recreate the partitioning scheme of <code>/dev/sda</code> on the new drive.

<pre class="text">sfdisk -d /dev/sda | fdisk /dev/sdb
</pre>
Then verify with <code>lsblk</code> or <code>fdisk -l</code>.

<pre class="text">mdadm --manage /dev/md0 --add /dev/sdb1
</pre>
<pre class="text">[root@lo4 ~]# mdadm --manage /dev/md0 --add /dev/sdb1
mdadm: added /dev/sdb1
</pre>
Finally, check the status of the rebuilding with

<pre class="text">cat /proc/mdstat
</pre>
<pre class="text">[root@lo4 ~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[0]
204736 blocks super 1.0 [2/1] [U_]
[===========>.........] recovery = 57.7% (118400/204736) finish=0.0min speed=118400K/sec

unused devices: <none>
</pre>
=== Missing Drive ===

In this example, <code>/dev/sda1</code> and <code>/dev/sdb1</code> make up the RAID 1 array <code>/dev/md0</code>. Let us say that <code>/dev/sdb1</code> is missing.

Use <code>lsblk</code> to examine HDD partitions with block sizes. Alternatively, you can use <code>fdisk -l</code> or any other utility you prefer.

Now check the status of <code>mdadm</code> with:

<pre class="text">cat /proc/mdstat
</pre>
<pre class="text">Personalities : [raid1]
md0 : active raid1 sdb1[1](F) sda1[0]
204736 blocks super 1.0 [2/1] [U_]

unused devices: <none>
</pre>
When a drive fails or is missing, you will see an underscore in the array output (<code>[U_]</code> instead of <code>[UU]</code>).

Use the output from <code>lsblk</code> and <code>/proc/mdsat</code> to match the present drive in an active <code>mdadm</code> array (<code>/dev/md0</code>) with the corresponding partition on the missing drive. For example, "match" <code>/dev/sda1</code> with <code>/dev/sdb1</code> (after verifying their block sizes are the same).

Now add <code>/dev/sdb1</code> back into the array:

<pre class="text">mdadm --manage /dev/md0 --add /dev/sdb1
</pre>
<pre class="text">[root@lo4 ~]# mdadm --manage /dev/md0 --add /dev/sdb1
mdadm: added /dev/sdb1
</pre>
You can view the status of the rebuilding array with:

<pre class="text">cat /proc/mdstat
</pre>
<pre class="text">[root@lo4 ~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[0]
204736 blocks super 1.0 [2/1] [U_]
[===========>.........] recovery = 57.7% (118400/204736) finish=0.0min speed=118400K/sec

unused devices: <none>
</pre>
== References and Resources ==

* http://www.howtoforge.com/replacing_hard_disks_in_a_raid1_array
* http://ubuntuforums.org/showthread.php?t=1760217
* https://raid.wiki.kernel.org/index.php/RAID_setup#RAID-1
* http://unix.stackexchange.com/questions/80501/no-etc-mdadm-conf-in-centos-6

Mdadm - Revision history

Craigje: Created page with "= Rebuilding and Creating RAID 1 Arrays with mdadm = == Crating Arrays == To create a mirrored array with two drives, sda and sdb, on partitions, <..."

Craigje: Created page with "= Rebuilding and Creating RAID 1 Arrays with mdadm = == Crating Arrays == To create a mirrored array with two drives, `sda` and `sdb`, on partitions, <..."