nas ~ # mdadm --verbose --manage --set-faulty /dev/md2 /dev/sdc2 mdadm: set /dev/sdc2 faulty in /dev/md2 nas ~ # mdadm -D /dev/md2 /dev/md2: Version : 1.2 Creation Time : Tue Aug 28 04:45:52 2012 Raid Level : raid5 Array Size : 78646272 (75.00 GiB 80.53 GB) Used Dev Size : 26215424 (25.00 GiB 26.84 GB) Raid Devices : 4 Total Devices : 6 Persistence : Superblock is persistent Update Time : Wed Dec 11 19:02:46 2013 State : active, degraded, recovering Active Devices : 3 Working Devices : 4 Failed Devices : 2 Spare Devices : 1 Layout : left-symmetric Chunk Size : 512K Rebuild Status : 4% complete Name : localhost.localdomain:2 UUID : a9d908f3:f8632fcf:59a69085:83d5f6aa Events : 10129 Number Major Minor RaidDevice State 0 8 3 0 active sync /dev/sda3 6 8 83 1 active sync /dev/sdf3 5 8 67 2 spare rebuilding /dev/sde3 4 8 18 3 active sync /dev/sdb2 1 8 50 - faulty /dev/sdd2 2 8 34 - faulty /dev/sdc2