pitSTOP

Creating a Mirrored RAID array

$ mdadm –create /dev/mdX –level=1 –raid-devices=2 /dev/sdY /dev/sdZ

- sdY , sdZ : partitions/disks taking part in the mirroring. They could be anything depending upon your situation. For ex, sdY could be sdc1 and sdZ could be sdf2

- mdX : name of the RAID partition on to which the partitions sdZ and sdZ are associated

Once the command is successfully executed, mdX will be listed in “/proc/partitions” as a partition. This can now be mounted and used a normal EXT2/3 partition. Now the partitions sdY and sdZ will contain exactly the same data.

info : To know the mirroring status as well as the health of the RAID arrays, do “cat /proc/mdstat” from command line. Output of the command is self-explanatory (else refer man pages).

Stopping the raid array

$ mdadm –manage –stop /dev/mdX

Use only one of the disks of the array

The disk/partition sdY or sdZ will not be mountable by themselves using mount command. For that, “assemble” a raid array with any one of the disk which you want, as given below:

$ mdadm –assemble –run /dev/mdX /dev/sdY

or

$ mdadm –assemble –run /dev/mdX /dev/sdZ

Remove/Wipe out only RAID array information from a disk

To remove a RAID array configuration from the disks participating in RAID, use the “–zero-superblock” option removes the RAID information from the partitions and hence the partition will no longer will be recognized as a RAID component. Individual partitions (ex. mdY, mdZ) can be mounted afterwards and data will be preserved.

$ mdadm /dev/mdX –stop # stop RAID

$mdadm /dev/mdX –zero-superblock /dev/sdY

or

$ mdadm /dev/mdX –zero-superblock /dev/sdZ

Re-creating RAID array with the drives (sdY/sdZ) whose superblock has been zeroed

Use the command for creating the RAID array. It will ask whether to create array with partitions containing ext2fs. Answer yes and the RAID array will be recreated. Existing data in the partitions will be preserved.

– acknowledgements to my friend jk for the info