[mdadm] 2 how-tos

1. how to cancel sync:

in order to cancel raid sync its necessary to left only one drive as active (we are talking about raid1):

 mdadm --fail /dev/md2 /dev/sda3

and  we will receive something like that (in my case it was md2 and /dev/sda3):

 mdadm --detail /dev/md2
/dev/md2:
        Version : 0.90
  Creation Time : Fri Feb  4 21:22:50 2011
     Raid Level : raid1
     Array Size : 1462766336 (1395.00 GiB 1497.87 GB)
  Used Dev Size : 1462766336 (1395.00 GiB 1497.87 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 2
    Persistence : Superblock is persistent

    Update Time : Tue Jan 10 18:37:27 2012
          State : clean, degraded
 Active Devices : 1
Working Devices : 1
 Failed Devices : 1
  Spare Devices : 0

           UUID : 71b91f85:bdd01b3f:776c2c25:004bd7b2
         Events : 0.28394

    Number   Major   Minor   RaidDevice State
       0       0        0        0      removed
       1       8       19        1      active sync   /dev/sdb3

       2       8        3        -      faulty spare   /dev/sda3

 /dev/sda3 was set as failed.

2. how to re-add failed disk into existing array and restart scan :)

• set disk as failed (we already did that in 1st how-to )
• remove device from array

mdadm --remove /dev/md2 /dev/sda3 

• add device one more time

mdadm --add /dev/md2/ /dev/sda3

We can check the status of the arrays on the system with:

watch -n .1 cat /proc/mdstat

 or

mdadm --detail /dev/md0