mdadm Quick Start Guide

Usage:

# mdadm [mode] <raiddevice> [options] <component-devices>

Assemble – Assemble previously created array into an active array

# mdadm -A -s	Scan and assembly all the RAID volume based on config file.
# mdadm -A /dev/md/imsm0 -e imsm /dev/ <member drives>	Assemble imsm0 container manually if without config file.
# mdadm -A /dev/md/md0 /dev/md/imsm0	Assemble md0 array manually if without config file.

Create/Grow/Misc – Create new array with metadata/change active size or number of active devices

# mdadm -C /dev/md/imsm0 /dev/nvme[0-3]n1 -n 4 -e imsm	Create imsm0 container with 4 nvme0-3 drives.
# mdadm -C /dev/md/md0 /dev/md/imsm0 -n 4 -l 5	Create md0 as 4DR5 in imsm0 container.
# mdadm -C /dev/md/md0 /dev/md/imsm0 - n 4 -l 5 --consistency- policy=ppl	Create md0 as 4DR5 in imsm0 container with RWH enabled.
# mdadm -C /dev/md/md0 /dev/md/imsm0 -n 4 -l 5 -z $((100*1024*1024))	Create 4DR5 with 100GB size for each drive. 300GB size created with this example command.
# mkfs.ext4 /dev/md/md0	Create ext4 filesystem in md0 RAID volume.
# mount /dev/md/md0 /mnt/<mountpoint>	Mount md0 RAID volume in the file system.
# mdadm -a /dev/md/imsm0 /dev/<nvmeXn1>	Add hot-spare drive to imsm0 container.
# mdadm -Ebs > /etc/mdadm.conf	Export device metadata to mdadm.conf file.
# mdadm -S /dev/md/md0	Stop and deactivate md0 array.
# mdadm -S /dev/md/imsm0	Stop and deactivate imsm0 container.
# mdadm -S -s	Stop and deactivate all.
# mdadm -f /dev/md/md0 /dev/nvme0n1	Fail nvme0n1 drive in md0 array.
# mdadm -r /dev/md/imsm0 /dev/nvme0n1	Detached nvme0n1 drive in imsm0 container.
# mdadm --zero-superblock /dev/nvme0n1	Clear and zero the superblock in nvme0n1 drive.
# mdadm -G /dev/md/md0 -l 0	Grow existing 2DR1 to 1DR0.
# mdadm -G /dev/md/imsm0 -n 2	Grow 2DR0 to container.
# mdadm -a /dev/md/imsm0 /dev/nvme2n1	Add one more drive into container.
# mdadm -G /dev/md/md0 -l 5 --layout=left-asymmetric	Grow 2DR0 to 3DR5.
# mdadm -G /dev/md/md0 --size=128G	Grow component size md0 to the 128GB.
# mdadm -G /dev/md/md0 --consistency-policy=resync	Switch RWH closure policy to resync on the running md0.
# mdadm -G /dev/md/md0 --consistency-policy=ppl	Enable RWH closure mechanism on the running md0.

Volume, Member, Hardware Information

# mdadm --detail-platform	Print detail of platform’s RAID capabilities.
# mdadm -D /dev/md/md0	Print detail of md0 device.
# mdadm -E /dev/nvme0n1	Print contents of metadata store in nvme0n1.
# cat /proc/mdstat	List all active md devices with information.

Follow/Monitor/Misc – Monitor one or more devices on state changes

# systemctl status mdmonitor.service	Check mdmonitor service.
# systemctl start mdmonitor.service	Start mdmonitor service.
# systemctl stop mdmonitor.service	Stop mdmonitor service.
# systemctl enable mdmonitor.service	Enable mdmonitor service for next boot auto start.