The following article is to show how to remove healthy partitions from software RAID1 devices to change the layout of the disk and then add them back to the array.
The mdadm is the tool to manipulate the software RAID devices under Linux and it is part of all Linux distributions (some don’t install it by default so it may need to be installed).
Software RAID layout
[root@srv ~]# cat /proc/mdstat
Personalities : [raid1]
md125 : active raid1 sda4[1] sdb3[0]
1047552 blocks super 1.2 [2/2] [UU]
bitmap: 0/1 pages [0KB], 65536KB chunk
md126 : active raid1 sdb2[0] sda3[1]
32867328 blocks super 1.2 [2/2] [UU]
md127 : active raid1 sda2[1] sdb1[0]
52427776 blocks super 1.2 [2/2] [UU]
bitmap: 0/1 pages [0KB], 65536KB chunk
unused devices: <none>
STEP 1) Make the partitions faulty.
The partitions cannot be removed if they are not faulty.
[root@srv ~]# mdadm --fail /dev/md125 /dev/sdb3 mdadm: set /dev/sdb3 faulty in /dev/md125 [root@srv ~]# mdadm --fail /dev/md126 /dev/sdb2 mdadm: set /dev/sdb2 faulty in /dev/md126 [root@srv ~]# mdadm --fail /dev/md127 /dev/sdb1 mdadm: set /dev/sdb1 faulty in /dev/md127
