CentOS / Redhat: Create Software RAID 1 Array
RAID devices are virtual devices created from two or more real block devices. Linux supports RAID1 and other levels. You need to have same size partition on both disks i.e. on second disk create partitions exactly the same size as those on the first disk, and set the type as fd (Linux raid autodetect). You need to use the following commands to create RAID 1.
WARNING! These examples may crash your computer or may result into data loss if not executed properly. These examples involves disk partition manipulation using the fdisk command and building (formatting) file systems using the mkfs.ext3 command. So make sure you backup all data before typing any one of the following command.
Our sample RAID -1 setup with two partitions:
+------------+
| |
| /dev/sda3 | ===============+
| | |
+------------+ |
37GB | =======> RAID-1 /dev/md0
|
+------------+ |
| | |
| /dev/sdb1 | ===============+
| |
+------------+
37GBStep # 1: List Partitions
Type the following commands:
# fdisk -l
# fdisk -l /dev/sda
Sample outputs:Disk /dev/sda: 73.2 GB, 73295462400 bytes
255 heads, 63 sectors/track, 8910 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 * 1 13 104391 83 Linux
/dev/sda2 14 3929 31455270 83 Linux
/dev/sda3 3930 8779 38957625 83 Linux
/dev/sda4 8780 8910 1052257+ 5 Extended
/dev/sda5 8780 8910 1052226 82 Linux swap / SolarisFor example, purpose you will use /dev/sda3 (size 37G). Now, list second disk partitions, enter:
# fdisk -l /dev/sdb
Sample outputs:Disk /dev/sdb: 73.2 GB, 73295462400 bytes
255 heads, 63 sectors/track, 8910 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id SystemStep # 2: Create 37G Partitions For /dev/sdb
Type the following command:
# fdisk /dev/sdb
Sample outputs:The number of cylinders for this disk is set to 8910.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(e.g., DOS FDISK, OS/2 FDISK)
Command (m for help):To add a new partition, type n command followed by p command as follows:
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-8910, default 1):
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-8910, default 8910): +37GTo print the partition table type p command, enter:
Command (m for help): p
Disk /dev/sdb: 73.2 GB, 73295462400 bytes
255 heads, 63 sectors/track, 8910 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdb1 1 37 297171 83 LinuxFinally, set partition type to "Software Raid" i.e. type 0xfd *(type t command followed by fd code to change partition type to Software RAID):
Command (m for help): t
Selected partition 1
Hex code (type L to list codes): fd
Command (m for help): p
Disk /dev/sdb: 73.2 GB, 73295462400 bytes
255 heads, 63 sectors/track, 8910 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdb1 1 37 297171 fd Linux raid autodetectSave the changes and exit to shell prompt by typing w command:
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.Step # 3: Create / Update 37G Partitions For /dev/sda
You need to delete /dev/sda3 (make sure you backup all data) and/or set it to software raid as follows using the fdisk command:
# fdisk /dev/sda
Sample outputs:The number of cylinders for this disk is set to 8910.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(e.g., DOS FDISK, OS/2 FDISK)
Command (m for help): p
Disk /dev/sda: 73.2 GB, 73295462400 bytes
255 heads, 63 sectors/track, 8910 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 * 1 13 104391 83 Linux
/dev/sda2 14 3929 31455270 83 Linux
/dev/sda3 3930 8779 38957625 83 Linux
/dev/sda4 8780 8910 1052257+ 5 Extended
/dev/sda5 8780 8910 1052226 82 Linux swap / Solaris
Command (m for help): t
Partition number (1-5): 3
Hex code (type L to list codes): fd
Changed system type of partition 3 to fd (Linux raid autodetect)
Command (m for help): p
Disk /dev/sda: 73.2 GB, 73295462400 bytes
255 heads, 63 sectors/track, 8910 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 * 1 13 104391 83 Linux
/dev/sda2 14 3929 31455270 83 Linux
/dev/sda3 3930 8779 38957625 fd Linux raid autodetect
/dev/sda4 8780 8910 1052257+ 5 Extended
/dev/sda5 8780 8910 1052226 82 Linux swap / Solaris
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table.
The new table will be used at the next reboot.
Syncing disks.Reload Partition Table Changes
Use the partprobe command to reload the changes without rebooting the box:
# partprobe /dev/sda
OR
# echo 1 > /sys/block/sdb/device/rescanStep #3: Create RAID 1 Array
To create RAID1 using /dev/sda3 and /dev/sdb1, enter:
# mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sda3 /dev/sdb1
To see RAID build progress, enter:
# watch cat /proc/mdstat
Sample outputs:
Fig.01: RAID 1 mirroring
Once build completed create a filesystem on the new software raid devices, enter:
# mkfs.ext3 /dev/md0mke2fs 1.39 (29-May-2006)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
4872896 inodes, 9737360 blocks
486868 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=4294967296
298 block groups
32768 blocks per group, 32768 fragments per group
16352 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
4096000, 7962624
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 39 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.Mount RAID1 at /raid1
Type the following commands:
# mkdir /raid1
# mount /dev/md0 /raid1/
# df -H /raid1/
Sample outputs:Filesystem Size Used Avail Use% Mounted on
/dev/md0 40G 185M 38G 1% /raid1How Do I Test My RAID 1 Array Speed?
Simply use the dd command as follows:
# cd /raid1/
# dd if=/dev/zero of=output bs=8k count=256k
# rm output262144+0 records in
262144+0 records out
2147483648 bytes (2.1 GB) copied, 6.01068 seconds, 357 MB/sUpdate /etc/fstab
Make sure RAID1 get mounted when you reboot the system (note >> append redirection):
# echo '/dev/md0 /raid1 ext3 noatime,rw 0 0' >> /etc/fstabHow Do I Get Detailed Information About RAID 1?
Type the following command:
# mdadm --query --detail /dev/md0
Sample outputs:/dev/md0:
Version : 0.90
Creation Time : Wed May 26 01:58:53 2010
Raid Level : raid1
Array Size : 38949440 (37.15 GiB 39.88 GB)
Used Dev Size : 38949440 (37.15 GiB 39.88 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Wed May 26 02:18:22 2010
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
UUID : b6f207e4:7f73484f:53f64bfd:e70b77d8
Events : 0.2
Number Major Minor RaidDevice State
0 8 3 0 active sync /dev/sda3
1 8 17 1 active sync /dev/sdb1