RAID: How to Set Up RAID 0, 1, 5 and 10 in CentOS&RedHat and Ubuntu&Debian!

 

This article explains how to set up (configure and manage) RAID 0, 1, 5 and 10 in CentOS, RedHat and UBUNTU/Debian.

Contents:

• RAID ?
• Set up RAID 0
• Set up RAID 1 :
• Set up RAID 5 :
• Set up RAID 10 :

 1- RAID?

       RAID (Redundant Array of Independent Disks, originally redundant array of inexpensive disks) is a storage technology that combines multiple disk drive components into a logical unit for the purposes of data redundancy and performance improvement, for more information.

 

Note 1: To manage the RAID with Linux, you should install raid manager (the manage MD devices aka Linux Software RAID)

• Verify the name of the RAID manager.

1- CentOS and RedHat:

# yum search raid
...
mdadm.i686 : The mdadm program controls Linux md devices (software RAID arrays)
...

2- UBUNTU and Debian:

 # apt-cache search raid
...
mdadm - tool to administer Linux MD arrays (software RAID)
....

• Install the mdadm (RAID Manager)

1- CentOS and RedHat:

# yum install mdadm

2- UBUNTU and Debian:

# apt-get install mdadm

 

Note 2: After configuration, if you want to make a permanent raid configuration through reboot.

# mdadm --detail -- scan >> /etc/mdadm.conf

  2- Set up RAID 0:

         RAID 0 (block-level striping without parity or mirroring) has no (or zero) redundancy. It provides improved performance and additional storage but no fault tolerance. Any drive failure destroys the array, and the likelihood of failure increases with more drives in the array, for more information.

RAID 0 (block-level striping)

I have two disks /dev/sdb and /dev/sdc with 1Gb each one.

• Verify the disks

# fdisk -l /dev/sdb
Disk /dev/sdb: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/sdb doesn't contain a valid partition table

 # fdisk -l /dev/sdc
Disk /dev/sdc: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/sdc doesn't contain a valid partition table

•  Create a RAID 0 (level 0) Disk (/dev/md0) with the disks /dev/sdb and /dev/sdc

# mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sdb /dev/sdc
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.

•  Verify the creation of the RAID 0 disk.

# mdadm --detail --scan
ARRAY /dev/md0 metadata=1.2 name=rhel:0 UUID=7b5ee535:1e1b850e:773566d3:7752d175

•  Verify also with RAID file under the proc directory

# cat /proc/mdstat
Personalities : [raid0]
md0 : active raid0 sdc[1] sdb[0]
      2095104 blocks super 1.2 512k chunks

unused devices: <none>

You can use LVM with /dev/md0 or you can create a partition with the command fdisk.

 # fdisk /dev/md0
WARNING: DOS-compatible mode is deprecated. It's strongly recommended to switch off the mode (command 'c') and change display units to sectors (command 'u').
Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-523776, default 257):
Using default value 257
Last cylinder, +cylinders or +size{K,M,G} (257-523776, default 523776):
Using default value 523776
Command (m for help): t
Selected partition 1
Hex code (type L to list codes): fd
Changed system type of partition 1 to fd (Linux raid autodetect)
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.

• To verify the size of the RAID 0 disk

# fdisk -l /dev/md0
Disk /dev/md0: 2145 MB, 2145386496 bytes
2 heads, 4 sectors/track, 523776 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 524288 bytes / 1048576 bytes
Disk identifier: 0xd2d27810
    Device Boot      Start         End      Blocks   Id  System
/dev/md0p1             257      523776     2094080   fd  Linux raid autodetect

• Create a file system on the first partion on the RAID 0 device

# mkfs.ext3 /dev/md0p1

3- Set up RAID 1:

In RAID 1 (mirroring without parity or striping), data is written identically to two drives, thereby producing a “mirrored set”, for more information.

 

RAID 1 (mirroring)

• I have two disks /dev/sdb and /dev/sdc with 1Gb each one.

# mdadm --create /dev/md1 --level=1 --raid-devices=2 /dev/sdb /dev/sdc
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md1 started.

•  Verify the creation

# mdadm --detail --scan
ARRAY /dev/md1 metadata=1.2 name=rhel:1 UUID=479fa3ed:c2317ac4:7a104152:6e96823e

• Verify also with RAID file under the proc directory

# cat /proc/mdstat
Personalities : [raid1]
md1 : active raid1 sdc[1] sdb[0]
      1048564 blocks super 1.2 [2/2] [UU]
unused devices: <none>

•  You can use LVM with /dev/md1 or you can create a partition with the command fdisk.

# fdisk /dev/md1

• To verify the size of the RAID 1 disk

# fdisk -l /dev/md1
Disk /dev/md1: 1073 MB, 1073729536 bytes
2 heads, 4 sectors/track, 262141 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xc842f68b
    Device Boot      Start         End      Blocks   Id  System
/dev/md1p1               1      262141     1048562   fd  Linux raid autodetect

 4- Set up RAID 5:

        RAID 5 (block-level striping with distributed parity) distributes parity along with the data and requires that all drives but one be present to operate. The array is not destroyed by a single drive failure. On drive failure, any subsequent reads can be calculated from the distributed parity such that the drive failure is masked from the end user. RAID 5 requires at least three disks, for more information.

RAID 5 (block-level striping with distributed parity)

I have three disks /dev/sdb, /dev/sdc and /dev/sdd with 1Gb each one.

# mdadm --create /dev/md5 --level=5 --raid-devices=3 /dev/sdb /dev/sdc /dev/sdd
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md5 started.

•  Verify also with RAID file uder the proc directory

mdadm --detail --scan
ARRAY /dev/md5 metadata=1.2 name=rhel:5 UUID=9e7113b6:2d5dc78d:db553d53:d6cc4555

• Verify the state of the RAID 5 disk with /dev/mdstat

# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md5 : active raid5 sdd[3] sdc[1] sdb[0]
      2096128 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU]
unused devices: <none>

•  Create a partition on the RAID5 disk

# fdisk /dev/md5

• Verify the disk size

# fdisk -l /dev/md5
Disk /dev/md5: 2146 MB, 2146435072 bytes
2 heads, 4 sectors/track, 524032 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 524288 bytes / 1048576 bytes
Disk identifier: 0x16b481fd
    Device Boot      Start         End      Blocks   Id  System
/dev/md5p1             257      524032     2095104   fd  Linux raid autodetec

• Add the disk /dev/sde  to RAID5, so the RAID disk will be with 4 disks.

# mdadm --manage /dev/md5 --add /dev/sde
mdadm: added /dev/sde

•  Verify the new state of the RAID disk

# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md5 : active raid5 sde[4](S) sdc[1] sdd[3] sdb[0]
      2096128 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU]

•  When we verify the new size, no changement

# fdisk -l /dev/md5
Disk /dev/md5: 2146 MB, 2146435072 bytes
2 heads, 4 sectors/track, 524032 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 524288 bytes / 1048576 bytes
Disk identifier: 0x16b481fd
    Device Boot      Start         End      Blocks   Id  System
/dev/md5p1             257      524032     2095104   fd  Linux raid autodetect

Note: The size is not increased!!

To increase the size, you shoud use the command mdadm with raid-devices or with max size options.

# mdadm --grow /dev/md5 --raid-devices=4
mdadm: Need to backup 3072K of critical section..

or

# mdadm --grow /dev/md5 –size max

•  to verify the reshape of the raid disk.  (you can use the command watch for  periodically showing the output with fullscreen: watch cat /proc/mdstat)

 # cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md5 : active raid5 sde[4] sdc[1] sdd[3] sdb[0]
      2096128 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/4] [UUUU]
      [==>..................]  reshape = 14.7% (154948/1048064) finish=4.5min speed=3265K/sec

unused devices: <none>

• You should wait…. When the reshape finish:

 # cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md5 : active raid5 sde[4] sdc[1] sdd[3] sdb[0]
      3144192 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/4] [UUUU]

unused devices: <none>

•  To verify the size of the disk /dev/md5

# mdadm --detail /dev/md5
/dev/md5:
        Version : 1.2
  Creation Time : Sat Nov  2 00:06:53 2013
     Raid Level : raid5
     Array Size : 3144192 (3.00 GiB 3.22 GB)
  Used Dev Size : 1048064 (1023.67 MiB 1073.22 MB)
   Raid Devices : 4
  Total Devices : 4
    Persistence : Superblock is persistent
    Update Time : Sat Nov  2 00:25:03 2013
          State : clean
 Active Devices : 4
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 0
         Layout : left-symmetric
     Chunk Size : 512K
           Name : rhel:5  (local to host rhel)
           UUID : 9e7113b6:2d5dc78d:db553d53:d6cc4555
         Events : 64
    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync   /dev/sdb
       1       8       32        1      active sync   /dev/sdc
       3       8       48        2      active sync   /dev/sdd
       4       8       64        3      active sync   /dev/sde

• Also you can verify the size with fdisk command:

# fdisk -l /dev/md5
Disk /dev/md5: 3219 MB, 3219652608 bytes
2 heads, 4 sectors/track, 786048 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 524288 bytes / 1048576 bytes
Disk identifier: 0x16b481fd
    Device Boot      Start         End      Blocks   Id  System
/dev/md5p1             257      524032     2095104   fd  Linux raid autodetect

• For Troubleshooting (Remove a disk from the RAID 5 disk ):

# mdadm --manage /dev/md5 --remove /dev/sdc

•  To stop RAID

# mdadm  -S  /dev/md5
# mdadm --zero-superblock /dev/sdb
# mdadm --zero-superblock /dev/sdc
# mdadm --zero-superblock /dev/sdd

5- Set up RAID 10:

A RAID 1+0, sometimes called RAID 1&0 or RAID 10, is similar to a RAID 0+1 with exception that the RAID levels used are reversed — RAID 10 is a stripe of mirrors, for more information.

RAID 10 (RAID 1&0)

I have four disks /dev/sdb, /dev/sdc, /dev/sdd and /dev/sde with 1Gb each one.

# mdadm --create /dev/md10 --level=10 --raid-devices=4 /dev/sdb /dev/sdc /dev/sdd /dev/sde
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md10 started.

•  To verify with the file mdstat

# cat /proc/mdstat
Personalities : [raid10]
md10 : active raid10 sde[3] sdd[2] sdc[1] sdb[0]
      2096128 blocks super 1.2 512K chunks 2 near-copies [4/4] [UUUU]
unused devices: <none>

• To verify the size

# mdadm --detail /dev/md10
/dev/md10:
        Version : 1.2
  Creation Time : Sat Nov  2 00:43:34 2013
     Raid Level : raid10
     Array Size : 2096128 (2047.34 MiB 2146.44 MB)
  Used Dev Size : 1048064 (1023.67 MiB 1073.22 MB)
   Raid Devices : 4
  Total Devices : 4
    Persistence : Superblock is persistent
    Update Time : Sat Nov  2 00:44:11 2013
          State : clean
 Active Devices : 4
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 0
         Layout : near=2
     Chunk Size : 512K
           Name : rhel:10  (local to host rhel)
           UUID : 43a7f30a:1f113564:2f264831:ccfb1d07
         Events : 17
    Number   Major   Minor   RaidDevice State
       0       8       16        0      active sync   /dev/sdb
       1       8       32        1      active sync   /dev/sdc
       2       8       48        2      active sync   /dev/sdd
       3       8       64        3      active sync   /dev/sde

 

Conclusion:

Configure RAID 0, 1, 5 and 10 in CentOS, RedHat and UBUNTU/Debian.