Creating Raid Group md0 with local disks:
This command creates a RAID5 device named /dev/md0, with 3 disks /dev/sdb /dev/sdc /dev/sdd.
mdadm: layout defaults to left-symmetric
mdadm: chunk size defaults to 64K
mdadm: array /dev/md0 started.
Details of device md0(/dev/md0) using fdisk
Once /dev/md0 is created, you should be able to see the details using fdisk.
Disk /dev/md0: 293.6 GB, 293631295488 bytes
2 heads, 4 sectors/track, 71687328 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Details of the md disk using mdadm command
/dev/md0:
Version : 00.90.03
Creation Time : Thu Sep 02 06:24:10 2008
Raid Level : raid5
Array Size : 286749312 (273.47 GiB 293.63 GB)
Used Dev Size : 143374656 (136.73 GiB 146.82 GB)
Raid Devices : 3
Total Devices : 3
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Thu Sep 02 07:01:44 2008
State : clean
Active Devices : 3
Working Devices : 3
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 64K
UUID : 0366e343:0366e343:0366e343:0366e343
Events : 0.2
Number Major Minor RaidDevice State
0 8 16 0 active sync /dev/sdb
1 8 32 1 active sync /dev/sdc
2 8 48 2 active sync /dev/sdd
How to keep /dev/md0 persistant across reboots?
Add the md device entry to /etc/mdadm.conf
ARRAY /dev/md0 level=raid5 num-devices=3 UUID=0366e343:0366e343:0366e343:0366e343
[root@foo15 ~]# mdadm -Es |grep md0 >> /etc/mdadm.conf
Adding a disk to /dev/md0
mdadm: added /dev/sde
/proc file for madadm : /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 sdb[0] sdd[2] sdc[1]
286749312 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]
unused devices: <none>
[root@foo15 proc]#