[root@sd /]# cat /proc/mdstat Personalities : [raid1] md0 : active raid1 sdb1[0] sda1[1] 7350592 blocks [2/2] [UU] unused devices: [root@sd /]# mdadm --fail /dev/md0 /dev/sda1 mdadm: set /dev/sda1 faulty in /dev/md0 [root@sd /]# mdadm -f /dev/md0 /dev/sda1 mdadm: set /dev/sda1 faulty in /dev/md0 [root@sd /]# mdadm --remove /dev/md0 /dev/sda1 mdadm: hot removed /dev/sda1 [root@sd /]# mdadm -r /dev/md0 /dev/sda1 mdadm: hot remove failed for /dev/sda1: No such device or address --- sda Pull out --- --- sda Plug in --- [root@sd /]# cat /proc/mdstat Personalities : [raid1] md0 : active raid1 sdb1[0] 7350592 blocks [2/1] [U_] unused devices: [root@sd /]# mdadm /dev/md0 --add /dev/sdc1 mdadm: re-added /dev/sdc1 [root@sd /]# cat /proc/mdstat Personalities : [raid1] md0 : active raid1 sdc1[2] sdb1[0] 7350592 blocks [2/1] [U_] [>....................] recovery = 0.6% (48064/7350592) finish=12.6min speed=9612K/sec unused devices: [root@sd /]# cat /proc/mdstat Personalities : [raid1] md0 : active raid1 sdc1[1] sdb1[0] 7350592 blocks [2/2] [UU] unused devices: [root@sd /]# fdisk /dev/sdb Command (m for help): p Disk /dev/sdb: 8010 MB, 8010072064 bytes 247 heads, 62 sectors/track, 1021 cylinders Units = cylinders of 15314 * 512 = 7840768 bytes Disk identifier: 0x00090b2c Device Boot Start End Blocks Id System /dev/sdb1 * 1 960 7350689 fd Linux raid autodetect /dev/sdb2 961 1021 467077 82 Linux swap / Solaris Command (m for help): q [root@sd /]# fdisk /dev/sdc Command (m for help): p Disk /dev/sdc: 8010 MB, 8010072064 bytes 247 heads, 62 sectors/track, 1021 cylinders Units = cylinders of 15314 * 512 = 7840768 bytes Disk identifier: 0x00064d12 Device Boot Start End Blocks Id System /dev/sdc1 * 1 960 7350689 fd Linux raid autodetect /dev/sdc2 961 1021 467077 82 Linux swap / Solaris Command (m for help): q [root@sd /]# free total used free shared buffers cached Mem: 497228 49380 447848 0 4164 26320 -/+ buffers/cache: 18896 478332 Swap: 934136 0 934136 [root@sd /]#