Sunday, September 29, 2013

mdadm to Configure RAID-Based

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

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:

/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

mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sda3 /dev/sdb1

=====================

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

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