# fdisk /dev/sda Command (m for help): p Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x699d5c03 Device Boot Start End Blocks Id System Command (m for help): n Command action e extended p primary partition (1-4) p Partition number (1-4): 1 First cylinder (1-60801, default 1): Using default value 1 Last cylinder, +cylinders or +size{K,M,G} (1-60801, default 60801): Using default value 60801 Command (m for help): t Selected partition 1 Hex code (type L to list codes): fd Changed system type of partition 1 to fd (Linux raid autodetect) Command (m for help): p Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x699d5c03 Device Boot Start End Blocks Id System /dev/sda1 1 60801 488384001 fd Linux raid autodetect Command (m for help): w The partition table has been altered! Calling ioctl() to re-read partition table. Syncing disks. [root@Bach ~]# fdisk /dev/sdc > SNIP Device Boot Start End Blocks Id System /dev/sdc1 1 60801 488384001 fd Linux raid autodetect >SNIP [root@Bach ~]# fdisk /dev/sdd >SNIP Device Boot Start End Blocks Id System /dev/sdd1 1 60801 488384001 fd Linux raid autodetect [root@Bach ~]# mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sda1 /dev/sdc1 /dev/sdd1 mdadm: layout defaults to left-symmetric mdadm: chunk size defaults to 64K mdadm: layout defaults to left-symmetric mdadm: super0.90 cannot open /dev/sda1: Device or resource busy mdadm: layout defaults to left-symmetric mdadm: super1.x cannot open /dev/sda1: Device or resource busy mdadm: ddf: Cannot use /dev/sda1: Device or resource busy mdadm: Cannot use /dev/sda1: It is busy mdadm: device /dev/sda1 not suitable for any style of array [root@Bach ~]# cat /etc/mtab /dev/sdb2 / ext3 rw 0 0 none /proc proc rw 0 0 none /proc/sys/fs/binfmt_misc binfmt_misc rw 0 0 gvfs-fuse-daemon /home/graeme/.gvfs fuse.gvfs-fuse-daemon rw,nosuid,nodev,user=graeme 0 0 [root@Bach ~]# cat /etc/fstab # Entry for /dev/sdb2 : UUID=f0c2de4f-422a-44bb-88d2-194c55dc127b / ext3 defaults 1 1 none /proc proc defaults 0 0 [root@Bach ~]# cat /proc/mdstat Personalities : [raid6] [raid5] [raid4] md127 : active raid5 sda[0] sdd[2] sdc[1] 976772992 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU] unused devices: [root@Bach ~]# mdadm --stop /dev/sda mdadm: /dev/sda does not appear to be an md device [root@Bach ~]# mdadm --stop /dev/sdc mdadm: /dev/sdc does not appear to be an md device [root@Bach ~]# mdadm --zero-superblock /dev/sda1 mdadm: Couldn't open /dev/sda1 for write - not zeroing [root@Bach ~]# mdadm --zero-superblock /dev/sda mdadm: Couldn't open /dev/sda for write - not zeroing [root@Bach ~]# mdadm -Q /dev/sda /dev/sda: is not an md array /dev/sda: device 0 in 3 device active raid5 /dev/md127. Use mdadm --examine for more detail. [root@Bach ~]# mdadm --examine /dev/sda /dev/sda: Magic : a92b4efc Version : 0.90.00 UUID : cc526422:3aae7bc9:d6030a07:261540d2 Creation Time : Wed Mar 17 15:53:39 2010 Raid Level : raid5 Used Dev Size : 488386496 (465.76 GiB 500.11 GB) Array Size : 976772992 (931.52 GiB 1000.22 GB) Raid Devices : 3 Total Devices : 3 Preferred Minor : 127 Update Time : Sun Mar 21 07:10:38 2010 State : clean Active Devices : 3 Working Devices : 3 Failed Devices : 0 Spare Devices : 0 Checksum : 60a86cd3 - correct Events : 50 Layout : left-symmetric Chunk Size : 64K Number Major Minor RaidDevice State this 0 8 0 0 active sync /dev/sda 0 0 8 0 0 active sync /dev/sda 1 1 8 32 1 active sync /dev/sdc 2 2 8 48 2 active sync /dev/sdd [root@Bach ~]#