Reducing mdadm Mirror Drive Count

“Grow” the array down to two devices:

$ sudo mdadm --grow /dev/md1 --raid-devices=2 --backup-file /tmp/mdadmbackup
raid_disks for /dev/md1 set to 2

Show the new status:

```$ sudo mdadm -D /dev/md1 /dev/md1: Version : 1.2 Creation Time : Fri Sep 16 22:38:10 2011 Raid Level : raid1 Array Size : 1953510841 (1863.01 GiB 2000.40 GB) Used Dev Size : 1953510841 (1863.01 GiB 2000.40 GB) Raid Devices : 2 Total Devices : 2 Persistence : Superblock is persistent

Update Time : Tue Jul  4 18:27:02 2017
      State : clean 

Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0

       Name : microserver:1  (local to host microserver)
       UUID : e19da472:04736a59:6c1e25ec:c4a60ebe
     Events : 20513

Number   Major   Minor   RaidDevice State
   3       8       49        0      active sync   /dev/sdd1
   2       8       17        1      active sync   /dev/sdb1

```

References:



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