====== RAID - mdadm - Growing an array ======

If a RAID is running out of space, additional disks can be added to the RAID to grow the array.

  * Multiple drives can be added in once to grow the RAID much bigger if needed.

<WRAP info>
**NOTE:**  The drive needs to be the same size as all the others of course.
</WRAP>

----

===== Initial Array =====

<code bash>
mdadm --detail /dev/md0
</code>

returns:

<code bash>
/dev/md0:
        Version : 1.2
  Creation Time : Tue Sep  6 18:31:41 2011
     Raid Level : raid6
     Array Size : 3144192 (3.00 GiB 3.22 GB)
  Used Dev Size : 1048064 (1023.67 MiB 1073.22 MB)
   Raid Devices : 5
  Total Devices : 5
    Persistence : Superblock is persistent

    Update Time : Thu Sep  8 18:54:26 2011
          State : clean
 Active Devices : 5
Working Devices : 5
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 512K

           Name : raidtest.loc:0  (local to host raidtest.loc)
           UUID : e0748cf9:be2ca997:0bc183a6:ba2c9ebf
         Events : 2058

    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync   /dev/sdb
       1       8       32        1      active sync   /dev/sdc
       5       8       48        2      active sync   /dev/sdd
       4       8       64        3      active sync   /dev/sde
       6       8       80        4      active sync   /dev/sdf
</code>

----

===== Add more drives =====

<code bash>
mdadm --add /dev/md0 /dev/sdg /dev/sdh
</code>

returns:

<code bash>
mdadm: added /dev/sdg
mdadm: added /dev/sdh
</code>

<WRAP info>
**NOTE:**  In this example 2 drives are added to the RAID.
</WRAP>


----

===== Grow the array =====

<code bash>
mdadm --grow /dev/md0 --raid-devices=7
</code>

returns:

<code bash>
mdadm: Need to backup 7680K of critical section..
</code>

----

===== Expand the File System Volume =====

A RAID device is like a hard drive.

  * Just because the hard drive is bigger, this does not mean the file system sees that extra space!
  * Therefore, the file system volume needs to be expanded.
  * This procedure has nothing to do with mdadm and is based on the file system.

<code bash>
resize2fs /dev/md0
</code>

returns:

<code bash>
resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/md0 is mounted on /mnt/md0; on-line resizing required
old desc_blocks = 1, new_desc_blocks = 1
Performing an on-line resize of /dev/md0 to 1310080 (4k) blocks.
The filesystem on /dev/md0 is now 1310080 blocks long.
</code>

----

===== Display Disks =====

<code bash>
df -hl
</code>

returns:

<code bash>
Filesystem            Size  Used Avail Use% Mounted on
...
/dev/md0              5.0G   70M  4.7G   2% /mnt/md0
</code>

----

===== Final Result =====

<code bash>
mdadm --detail /dev/md0
</code>

returns:

<code bash>
/dev/md0:
        Version : 1.2
  Creation Time : Tue Sep  6 18:31:41 2011
     Raid Level : raid6
     Array Size : 5240320 (5.00 GiB 5.37 GB)
  Used Dev Size : 1048064 (1023.67 MiB 1073.22 MB)
   Raid Devices : 7
  Total Devices : 7
    Persistence : Superblock is persistent

    Update Time : Thu Sep  8 19:01:15 2011
          State : clean
 Active Devices : 7
Working Devices : 7
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 512K

           Name : raidtest.loc:0  (local to host raidtest.loc)
           UUID : e0748cf9:be2ca997:0bc183a6:ba2c9ebf
         Events : 2089

    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync   /dev/sdb
       1       8       32        1      active sync   /dev/sdc
       5       8       48        2      active sync   /dev/sdd
       4       8       64        3      active sync   /dev/sde
       6       8       80        4      active sync   /dev/sdf
       8       8      112        5      active sync   /dev/sdh
       7       8       96        6      active sync   /dev/sdg
</code>

<WRAP info>
**NOTE:**  The RAID size has been increased, without ever bringing the file system offline.

  * There could be VMs or any other data running on the RAID during any of these procedures.

</WRAP>

----