Installation guide

3. Using mdadm to Configure RAID-Based and
Multipath Storage
Similar to other tools comprising the raidtools package set, the mdadm command can be used to
perform all the necessary functions related to administering multiple-device sets. This section
explains how mdadm can be used to:
• Create a RAID device
• Create a multipath device
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:
• /dev/sda1
• /dev/sdb1
• /dev/sdc1
• /dev/sdd1
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
3.1. Creating a RAID Device With mdadm
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