===== Create \ Start \ Stop Arrays =====
==== Create a RAID 1 device ====
  mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/{left,right}_raid1

==== RAID 5 ====
  mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/sdd1 /dev/sdc1 /dev/sdb1

==== Create a degraded RAID device with a missing drive ====
You can create a RAID device with a missing drive by giving missing in place of the device
  * mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/left_raid1 missing
==== Stop / Start an array ====
  * mdadm -S /dev/md1
  * <del> mdadm -R /dev/md1 </del>
  * After an array is stopped, and you want to start it backup up, you must first assemble the array

==== Re Assemble a RAID device ====
If you have a /etc/mdadm.conf file you can just
  * mdadm -A /dev/md0
If you don't have an mdadm.conf file then you will need to specify the partitions
  * mdadm -v -A /dev/md0 /dev/left_raid1 /dev/right_raid

===== details about a RAID device =====
  * mdadm -D /dev/md0
  * cat /proc/mdstat


===== Set disk faulty and remove =====
==== Set disk faulty ====
  * mdadm --set-faulty /dev/md0 /dev/right_raid1
    * mdadm: set /dev/right_raid1 faulty in /dev/md0
==== Remove drive ====
  * mdadm /dev/md0 -r /dev/right_raid1
    * mdadm: hot removed /dev/right_raid1
==== Add a replacement drive in ====
  * mdadm /dev/md0 -a /dev/right_raid1
    * mdadm: re-added /dev/right_raid1
==== To add the same drive back in ===
  * mdadm --re-add /dev/md1 /dev/right_raid1
===== Add a spare =====
  * mdadm /dev/md0 -a /dev/sdd2
    * mdadm: added /dev/sdd2
If a disk is partitioned, and you can't reboot use partprobe

===== Various Commands =====
Stop an array
  * mdadm -S /dev/md1

**Re Assemble a RAID device**
  * <code>mdadm -v -A /dev/md0 /dev/left_raid1 /dev/right_raid</code>
** Send a test message to make sure the monitoring is working **
  * <code>mdadm --monitor -t --scan -1 </code>

===== Links =====
  * http://linux-raid.osdl.org/index.php/Linux_Raid
  * [[ http://www.ducea.com/2009/03/08/mdadm-cheat-sheet/#more-691 | MDADM Cheat sheet ]]
  * [[ http://archives.free.net.ph/message/20071113.172054.ddbf71f7.en.html | Stride, stripe, chunk-size ]]

===== Change sync speed =====
  * /proc/sys/dev/raid/speed_limit_min
  * /proc/sys/dev/raid/speed_limit_max
  
===== mdadm.conf =====
  mdadm --detail --scan >> /etc/mdadm/mdadm.conf
  mdadm --examine --scan >> /etc/mdadm/mdadm.conf