mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/{left,right}_raid1

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

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

• mdadm -S /dev/md1
• mdadm -R /dev/md1
• After an array is stopped, and you want to start it backup up, you must first assemble the array

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

• mdadm -D /dev/md0
• cat /proc/mdstat

• mdadm –set-faulty /dev/md0 /dev/right_raid1
  • mdadm: set /dev/right_raid1 faulty in /dev/md0

• mdadm /dev/md0 -r /dev/right_raid1
  • mdadm: hot removed /dev/right_raid1

• mdadm /dev/md0 -a /dev/right_raid1
  • mdadm: re-added /dev/right_raid1

• mdadm –re-add /dev/md1 /dev/right_raid1

• mdadm /dev/md0 -a /dev/sdd2
  • mdadm: added /dev/sdd2

If a disk is partitioned, and you can't reboot use partprobe

Stop an array

• mdadm -S /dev/md1

Re Assemble a RAID device

• mdadm -v -A /dev/md0 /dev/left_raid1 /dev/right_raid

Send a test message to make sure the monitoring is working

• mdadm --monitor -t --scan -1 

• http://linux-raid.osdl.org/index.php/Linux_Raid
• MDADM Cheat sheet
• Stride, stripe, chunk-size

• /proc/sys/dev/raid/speed_limit_min
• /proc/sys/dev/raid/speed_limit_max

mdadm --detail --scan >> /etc/mdadm/mdadm.conf
mdadm --examine --scan >> /etc/mdadm/mdadm.conf