Systems

SATA/SCSI Hot plugging

Scan SCSI bus for hot plugged devices:

echo "- - -" > /sys/class/scsi_host/host<HOST>/scan

Spin down a device before hot plug removal:

echo 1 > /sys/block/<DEVICE>/device/delete

Taken from mdadm cheat sheet[1]

Creates a new array:
This creates a new level 1 (mirrored) array over two devices - sda and sdb.

mdadm --create --verbose /dev/md0 --level=1 /dev/sda1 /dev/sdb2

Write the configuration:

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

Remove a disk from an array:
The disk needs to be failed first before it can be removed, although it's most likely in a failed state already.

mdadm --fail /dev/md0 /dev/sda1

and now remove it

mdadm --remove /dev/md0 /dev/sda1

Add a disk to an existing array:
The partition table will probably have to be recreated.

sfdisk -d /dev/<ORIGINAL> | sfdisk /dev/<NEW>

then add the device to the array.

mdadm --add /dev/md0 /dev/sdb1

Verifying the status of the RAID arrays:

cat /proc/mdstat

or

mdadm --detail /dev/md0