[root@localhost testraid]# mdadm --detail /dev/md1
/dev/md1:
        Version : 0.90
  Creation Time : Sat May 15 18:45:50 2010
     Raid Level : raid6
     Array Size : 4194048 (4.00 GiB 4.29 GB)
  Used Dev Size : 1048512 (1024.11 MiB 1073.68 MB)
   Raid Devices : 6
  Total Devices : 6
Preferred Minor : 1
    Persistence : Superblock is persistent

    Update Time : Sat May 15 19:27:26 2010
          State : clean
 Active Devices : 6
Working Devices : 6
 Failed Devices : 0
  Spare Devices : 0

     Chunk Size : 64K

           UUID : 93e97ff0:aef3344b:bfe78010:bc810f04 (local to host localhost.localdomain)
         Events : 0.80

    Number   Major   Minor   RaidDevice State
       0       7       10        0      active sync   /dev/loop10
       1       7       11        1      active sync   /dev/loop11
       2       7       12        2      active sync   /dev/loop12
       3       7       13        3      active sync   /dev/loop13
       4       7       14        4      active sync   /dev/loop14
       5       7       15        5      active sync   /dev/loop15

[root@localhost testraid]# cat /proc/mdstat 
Personalities : [raid6] [raid5] [raid4] 
md1 : active raid6 loop13[3] loop11[1] loop15[5] loop14[4] loop12[2] loop10[0]
      4194048 blocks level 6, 64k chunk, algorithm 2 [6/6] [UUUUUU]
      
unused devices: 

[root@localhost testraid]# dd if=/dev/zero bs=4096 of=file 
dd: writing `file': No space left on device
1013618+0 records in
1013617+0 records out
4151775232 bytes (4.2 GB) copied, 28.6556 s, 145 MB/s

[root@localhost testraid]# mdadm --fail /dev/md1 /dev/loop14
mdadm: set /dev/loop14 faulty in /dev/md1

[root@localhost testraid]# dd if=/dev/zero bs=4096 of=/dev/loop14 
dd: writing `/dev/loop14': No space left on device
262145+0 records in
262144+0 records out
1073741824 bytes (1.1 GB) copied, 3.36093 s, 319 MB/s

[root@localhost testraid]# mdadm --remove /dev/md1 /dev/loop14
mdadm: hot removed /dev/loop14

[root@localhost testraid]# mdadm --add /dev/md1 /dev/loop14
mdadm: added /dev/loop14

[root@localhost testraid]# cat /proc/mdstat 
Personalities : [raid6] [raid5] [raid4] 
md1 : active raid6 loop14[6] loop13[3] loop11[1] loop15[5] loop12[2] loop10[0]
      4194048 blocks level 6, 64k chunk, algorithm 2 [6/5] [UUUU_U]
      [===>.................]  recovery = 18.9% (199620/1048512) finish=0.2min speed=66540K/sec
      
unused devices: 

[root@localhost testraid]# cat /proc/mdstat 
Personalities : [raid6] [raid5] [raid4] 
md1 : active raid6 loop14[4] loop13[3] loop11[1] loop15[5] loop12[2] loop10[0]
      4194048 blocks level 6, 64k chunk, algorithm 2 [6/6] [UUUUUU]
      
unused devices: 

[root@localhost testraid]# dd if=file bs=4096 of=/dev/null
1013617+0 records in
1013617+0 records out
4151775232 bytes (4.2 GB) copied, 16.5749 s, 250 MB/s
[root@localhost testraid]#