22.3.1. Creating a RAID Device With mdadm

22.3.1. Creating a RAID Device With mdadm

To create a RAID device, edit the /etc/mdadm.conf file to define appropriate DEVICE and ARRAY values:

DEVICE /dev/sd[abcd]1
ARRAY /dev/md0 devices=/dev/sda1,/dev/sdb1,/dev/sdc1,/dev/sdd1

In this example, the DEVICE line is using traditional file name globbing (refer to the glob(7) man page for more information) to define the following SCSI devices:

The ARRAY line defines a RAID device (/dev/md0) that is comprised of the SCSI devices defined by the DEVICE line.

Prior to the creation or usage of any RAID devices, the /proc/mdstat file shows no active RAID devices:

Personalities :
read_ahead not set
Event: 0
unused devices: none

Next, use the above configuration and the mdadm command to create a RAID 0 array:

mdadm -C /dev/md0 --level=raid0 --raid-devices=4 /dev/sda1 /dev/sdb1 /dev/sdc1 \
/dev/sdd1
Continue creating array? yes
mdadm: array /dev/md0 started.

Once created, the RAID device can be queried at any time to provide status information. The following example shows the output from the command mdadm --detail /dev/md0:

/dev/md0:
Version : 00.90.00
Creation Time : Mon Mar  1 13:49:10 2004
Raid Level : raid0
Array Size : 15621632 (14.90 GiB 15.100 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 0
Persistence : Superblock is persistent

Update Time : Mon Mar  1 13:49:10 2004
State : dirty, no-errors
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0

Chunk Size : 64K

      Number   Major   Minor   RaidDevice State
         0       8        1        0      active sync   /dev/sda1
         1       8       17        1      active sync   /dev/sdb1
         2       8       33        2      active sync   /dev/sdc1
         3       8       49        3      active sync   /dev/sdd1
           UUID : 25c0f2a1:e882dfc0:c0fe135e:6940d932
         Events : 0.1

Note: This documentation is provided {and copyrighted} by Red Hat®, Inc. and is released via the Open Publication License. The copyright holder has added the further requirement that Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder. The CentOS project redistributes these original works (in their unmodified form) as a reference for CentOS-5 because CentOS-5 is built from publicly available, open source SRPMS. The documentation is unmodified to be compliant with upstream distribution policy. Neither CentOS-5 nor the CentOS Project are in any way affiliated with or sponsored by Red Hat®, Inc.