Linux & RAID - very simple how to
Everything You Always Wanted to Know About RAID in Linux But Were Afraid to Ask
What you need:
mdadm
mdadm is a tool for managing Linux Software RAID arrays, it can create, assemble, report on, and monitor arrays.
You cant find in your distro (use your distro’s package manager to install it) or at: http://neilb.web.cse.unsw.edu.au/source/mdadm/ or http://www.kernel.org/pub/linux/utils/raid/mdadm/ or any of the kernel.org mirrors.
What you need to do:
You need some basic knowledge what RAID is - read about RAID at Wikipedia.
OK, now you know what RAID is.
You need to know “why do I need RAID on my Linux?”
Let’s assume you have two hard disks and need to boost up your disk performance (generally boost up your Linux performance).
So… you need RAID 0 should be your choice.
A RAID 0 (also known as a stripe set or striped volume) splits data evenly across two or more disks with no parity information for redundancy. RAID 0 is usually used to increase performance.
A RAID 0 can be created with disks (or disks partitions) of differing sizes, but the storage space added to the array by each disk/partition is limited to the size of the smallest disk—for example, if a 120 GB disk is striped together with a 100 GB disk, the size of the array will be 2*100 GB = 200 GB.
You need to create two partitions - lets assume you have two hard disks (hda and hdb) with about 100GB free space on each. To make RAID partition you need to create two partitions (one on hda and second one on hdb).
Warning: make some backup of your data before making any change on your hard disks.
So… using your fdisk tool (or any other you know) create 100GB’s partitions.
Creating RAID:
now you have two partitions
(for example):
hda3 & hdb2
to create RAID 0 and name it md0 type:
mdadm --create --verbose /dev/md0 --level=0 --raid-devices=2 /dev/hda3 /dev/hdb2
now you should make some file system on it (using mkfs command).
To create reiserfs system on your RAID partition type:
mkfs.reiserfs /dev/md0
if you prefer ext3 type:
mkfs.ext3 /dev/md0
Now (depending of your Linux distro) you could create mdadm.conf file, type:
mdadm --detail --scan >> /etc/mdadm.conf
or
mdadm --detail --scan >> /etc/mdadm/mdadm.conf (depending of your distro)
Finally you should mount your new RAID partition:
Let’s assume you want your RAID partition at /mnt/data and your filesystem is reiserfs
edit /etc/fstab file and add one line
/dev/md0 /mnt/data reiserfs defaults 0 1
Now you can restart your Linux machine or type:
mount /dev/md0
or
mount /mnt/data
That’s all!
Some usefull tips:
to check existing RAID partitions type:
mdadm --detail --scan
sample output:
ARRAY /dev/md1 level=raid0 num-devices=2 UUID=23229fa7:ae5e4cbb:e44dc3ab:a74065bb
ARRAY /dev/md0 level=raid0 num-devices=2 UUID=97fa925a:8164e2cf:327e4a2c:de536eaa
to start RAID partition from LiveCD:
mdadm -A /dev/md0 /dev/hda3 /dev/hdb2
to check details of selected RAID partition type:
mdadm --detail /dev/md0
sample output:
/dev/md0: Update Time : Wed Aug 30 21:02:19 2006
Version : 00.90.03
Creation Time : Wed Aug 30 21:02:19 2006
Raid Level : raid0
Array Size : 19550848 (18.65 GiB 20.02 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 0
Persistence : Superblock is persistent
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Chunk Size : 64K
UUID : 97fa925a:8164e2cf:327e4a2c:de536eaa
Events : 0.1
Number Major Minor RaidDevice State
0 3 6 0 active sync /dev/hda6
1 8 1 1 active sync /dev/sda1
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