изъять диск из raid-массива

root@fiserver:/mnt# mdadm --misc -D /dev/md3
/dev/md3:
        Version : 1.2
  Creation Time : Fri Aug 19 09:26:50 2016
     Raid Level : raid10
     Array Size : 195178496 (186.14 GiB 199.86 GB)
  Used Dev Size : 97589248 (93.07 GiB 99.93 GB)
   Raid Devices : 4
  Total Devices : 3
    Persistence : Superblock is persistent

    Update Time : Fri Feb 10 12:10:41 2017
          State : clean, degraded
 Active Devices : 3
Working Devices : 3
 Failed Devices : 0
  Spare Devices : 0

         Layout : near=2
     Chunk Size : 512K

           Name : fiserver:3  (local to host fiserver)
           UUID : f2a21247:285a58a3:c4fcc7d4:87fe526d
         Events : 3014187

    Number   Major   Minor   RaidDevice State
       0       8        5        0      active sync set-A   /dev/sda5
       4       8       17        1      active sync set-B   /dev/sdb1
       5       8       38        2      active sync set-A   /dev/sdc6
       6       0        0        6      removed

root@fiserver:/mnt# mdadm /dev/md3 --fail /dev/sdc6 --remove /dev/sdc6
mdadm: set device faulty failed for /dev/sdc6:  Device or resource busy