mdadm Linux Software RAID QuickStart Guide

Create New RAID 1 Array:

First setup your partitions (make sure they are exactly the same size)
In my example I have sda3 and sdb3 which are 500GB in size.

mdadm --create /dev/md2 --level=1 --raid-devices=2 /dev/sda3 /dev/sdb3
mdadm: array /dev/md2 started.

Check Status Of The Array

*Note I already have other arrays md0 and md1.

You can see below that md2 is syncing at a speed of about 91MB per sec.

cat /proc/mdstat

Personalities : [raid1]
md2 : active raid1 sdb3[1] sda3[0]
488287552 blocks [2/2] [UU]
[>....................] resync = 0.5% (2460992/488287552) finish=88.8min speed=91147K/sec

md1 : active raid1 sda2[0] sdb2[1]
29302464 blocks [2/2] [UU]

md0 : active raid1 sdb1[1] sda1[0]
58604992 blocks [2/2] [UU]

unused devices:

Check the basic details of an array:

mdadm /dev/md0
/dev/md0: 55.89GiB raid1 2 devices, 0 spares. Use mdadm --detail for more detail.
/dev/md0: No md super block found, not an md component.

More Detail

mdadm --detail /dev/md0

Version : 0.90
Creation Time : Tue Aug 31 22:37:52 2010
Raid Level : raid1
Array Size : 58604992 (55.89 GiB 60.01 GB)
Used Dev Size : 58604992 (55.89 GiB 60.01 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 0
Persistence : Superblock is persistent

Update Time : Wed Sep 1 18:39:53 2010
State : active
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

UUID : 7b4e9a42:823c7ee5:0d6ee1b8:30df68a8
Events : 0.7

Number Major Minor RaidDevice State
0 8 1 0 active sync /dev/sda1
1 8 17 1 active sync /dev/sdb1

Update /etc/mdadm.conf File

mdadm --brief --detail /dev/md0

ARRAY /dev/md0 level=raid1 num-devices=2 metadata=0.90 UUID=7b4e9a42:823c7ee5:0d6ee1b8:30df68a8

To edit the /etc/mdadm.conf file directly just run the command like this make sure to use the ">>" or you will wipe out any existing array info.

mdadm --brief --detail /dev/md0 >> /etc/mdadm.conf


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