RAID 0,RAID 1,RAID 5,Explained with Diagrams:

RAID, means Redundant Array of Independent Disks (originally Redundant Array of Inexpensive Disks), is a storage technology that provides increased reliability and functions through redundancy. This is achieved by combining multiple disk drive components into a logical unit, where data is distributed across the drives in one of several ways called "RAID levels"; RAID can be handled either by the operating system software or it may be implemented via a purpose built RAID disk controller card without having to configure the operating system at all.

On most situations you will be using one of the following four levels of RAIDs.

RAID 0
RAID 1
RAID 5

In the figure A, B, C, D, E and F – represents blocks and p1, p2, and p3 – represents parity

RAID level 0 – Striping

In a RAID 0 system data are split up in blocks that get written across all the drives in the array. By using multiple disks (at least 2) at the same time, this offers superior I/O performance. This performance can be enhanced further by using multiple controllers, ideally one controller per disk.

Advantages

RAID 0 offers great performance, both in read and write operations. There is no overhead caused by parity controls.
All storage capacity is used, there is no disk overhead.
The technology is easy to implement.

Disadvantages

RAID 0 is not fault-tolerant. If one disk fails, all data in the RAID 0 array are lost. It should not be used on mission-critical systems.

Ideal use

RAID 0 is ideal for non-critical storage of data that have to be read/written at a high speed, such as on a Photoshop image retouching station.

RAID level 1 – Mirroring

Data are stored twice by writing them to both the data disk (or set of data disks) and a mirror disk (or set of disks) . If a disk fails, the controller uses either the data drive or the mirror drive for data recovery and continues operation. You need at least 2 disks for a RAID 1 array.

RAID 1 systems are often combined with RAID 0 to improve performance. Such a system is sometimes referred to by the combined number: a RAID 10 system.

Advantages

RAID 1 offers excellent read speed and a write-speed that is comparable to that of a single disk.
In case a disk fails, data do not have to be rebuild, they just have to be copied to the replacement disk.
RAID 1 is a very simple technology.

Disadvantages

The main disadvantage is that the effective storage capacity is only half of the total disk capacity because all data get written twice.
Software RAID 1 solutions do not always allow a hot swap of a failed disk (meaning it cannot be replaced while the server keeps running). Ideally a hardware controller is used.

Ideal use

RAID-1 is ideal for mission critical storage, for instance for accounting systems. It is also suitable for small servers in which only two disks will be used.

RAID level 3

On RAID 3 systems, data blocks are subdivided (striped) and written in parallel on two or more drives. An additional drive stores parity information. You need at least 3 disks for a RAID 3 array.

Since parity is used, a RAID 3 stripe set can withstand a single disk failure without losing data or access to data.

Advantages

RAID-3 provides high throughput (both read and write) for large data transfers.
Disk failures do not significantly slow down throughput.

Disadvantages

This technology is fairly complex and too resource intensive to be done in software.
Performance is slower for random, small I/O operations.

Ideal use

RAID 3 is not that common in prepress.

RAID level 5

RAID 5 is the most common secure RAID level. It is similar to RAID-3 except that data are transferred to disks by independent read and write operations (not in parallel). The data chunks that are written are also larger. Instead of a dedicated parity disk, parity information is spread across all the drives. You need at least 3 disks for a RAID 5 array.
A RAID 5 array can withstand a single disk failure without losing data or access to data. Although RAID 5 can be achieved in software, a hardware controller is recommended. Often extra cache memory is used on these controllers to improve the write performance.

Advantages

Read data transactions are very fast while write data transaction are somewhat slower (due to the parity that has to be calculated).

Disadvantages

Disk failures have an effect on throughput, although this is still acceptable.
Like RAID 3, this is complex technology.

Ideal use

RAID 5 is a good all-round system that combines efficient storage with excellent security and decent performance. It is ideal for file and application servers.

RAID level 10 – Combining RAID 0 & RAID 1

RAID 10 combines the advantages (and disadvantages) of RAID 0 and RAID 1 in one single system. It provides security by mirroring all data on a secondary set of disks (disk 3 and 4 in the drawing below) while using striping across each set of disks to speed up data transfers.

Necessary command for RAID :

[root@localhost ~]# parted /dev/hda
GNU Parted 1.8.1
Using /dev/hda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) print free

Model: SAMSUNG SP0802N (ide)
Disk /dev/hda: 80.1GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number Start   End     Size    Type      File system Flags
1      32.3kB 22.7GB 22.7GB primary   ntfs         boot
2      22.7GB 80.1GB 57.3GB extended
5      22.7GB 54.3GB 31.6GB logical   ntfs
6      54.3GB 70.0GB 15.7GB logical   ext3
7      70.0GB 70.8GB 732MB   logical   linux-swap
8      70.8GB 71.0GB 206MB   logical   ext2
        71.0GB 80.1GB 9089MB            Free Space

[root@localhost ~]# fdisk -l

Disk /dev/hda: 80.0 GB, 80060424192 bytes
255 heads, 63 sectors/track, 9733 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id System
/dev/hda1   *           1        2764    22201798+   7 HPFS/NTFS
/dev/hda2            2765        9733    55978492+   5 Extended
/dev/hda5            2765        6602    30828703+   7 HPFS/NTFS
/dev/hda6            6603        8514    15358108+ 83 Linux
/dev/hda7            8515        8603      714861   82 Linux swap / Solaris
/dev/hda8            8604        8628      200781   83 Linux

[root@localhost ~]# df -h
Filesystem            Size Used Avail Use% Mounted on
/dev/hda6              15G 7.1G 6.5G 53% /
tmpfs                 124M     0 124M   0% /dev/shm
/dev/hda8             190M 1.6M 179M   1% /saifulpartion

RAID Configuration for Linux :

[root@localhost ~]# fdisk /dev/hda

The number of cylinders for this disk is set to 9733.
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): n (Creat New partition)
Command action
   l   logical (5 or over)
   p   primary partition (1-4)
l(For logical Partition)
First cylinder (8629-9733, default 8629):Press Enter
Using default value 8629
Last cylinder or +size or +sizeM or +sizeK (8629-9733, default 9733): +500M(Partition size in MB)

Command (m for help): n
Command action
   l   logical (5 or over)
   p   primary partition (1-4)
l
First cylinder (8691-9733, default 8691):
Using default value 8691
Last cylinder or +size or +sizeM or +sizeK (8691-9733, default 9733): +500M

Command (m for help): n
Command action
   l   logical (5 or over)
   p   primary partition (1-4)
l
First cylinder (8753-9733, default 8753):
Using default value 8753
Last cylinder or +size or +sizeM or +sizeK (8753-9733, default 9733): +500M

Command (m for help): w(Press w for save)
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.
[root@localhost ~]# partprobe /dev/hda(For )
[root@localhost ~]# partprobe /dev/hda
[root@localhost ~]# partprobe /dev/hda

[root@localhost ~]# fdisk -l(For check Newly create partition)

Disk /dev/hda: 80.0 GB, 80060424192 bytes
255 heads, 63 sectors/track, 9733 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id System
/dev/hda1   *           1        2764    22201798+   7 HPFS/NTFS
/dev/hda2            2765        9733    55978492+   5 Extended
/dev/hda5            2765        6602    30828703+   7 HPFS/NTFS
/dev/hda6            6603        8514    15358108+ 83 Linux
/dev/hda7            8515        8603      714861   82 Linux swap / Solaris
/dev/hda8            8604        8628      200781   83 Linux
/dev/hda9            8629        8690      497983+ 83 Linux
/dev/hda10           8691        8752      497983+ 83 Linux
/dev/hda11           8753        8814      497983+ 83 Linux

Command (m for help): L(For Search ID)

0 Empty           1e Hidden W95 FAT1 80 Old Minix       bf Solaris
1 FAT12           24 NEC DOS         81 Minix / old Lin c1 DRDOS/sec (FAT-
2 XENIX root      39 Plan 9          82 Linux swap / So c4 DRDOS/sec (FAT-
3 XENIX usr       3c PartitionMagic 83 Linux           c6 DRDOS/sec (FAT-
4 FAT16 <32M      40 Venix 80286     84 OS/2 hidden C: c7 Syrinx
5 Extended        41 PPC PReP Boot   85 Linux extended da Non-FS data
6 FAT16           42 SFS             86 NTFS volume set db CP/M / CTOS / .
7 HPFS/NTFS       4d QNX4.x          87 NTFS volume set de Dell Utility
8 AIX             4e QNX4.x 2nd part 88 Linux plaintext df BootIt
9 AIX bootable    4f QNX4.x 3rd part 8e Linux LVM       e1 DOS access
a OS/2 Boot Manag 50 OnTrack DM      93 Amoeba          e3 DOS R/O
b W95 FAT32       51 OnTrack DM6 Aux 94 Amoeba BBT      e4 SpeedStor
c W95 FAT32 (LBA) 52 CP/M            9f BSD/OS          eb BeOS fs
e W95 FAT16 (LBA) 53 OnTrack DM6 Aux a0 IBM Thinkpad hi ee EFI GPT
f W95 Ext'd (LBA) 54 OnTrackDM6      a5 FreeBSD         ef EFI (FAT-12/16/
10 OPUS            55 EZ-Drive        a6 OpenBSD         f0 Linux/PA-RISC b
11 Hidden FAT12    56 Golden Bow      a7 NeXTSTEP        f1 SpeedStor
12 Compaq diagnost 5c Priam Edisk     a8 Darwin UFS      f4 SpeedStor
14 Hidden FAT16 <3 61 SpeedStor       a9 NetBSD          f2 DOS secondary
16 Hidden FAT16    63 GNU HURD or Sys ab Darwin boot     fb VMware VMFS
17 Hidden HPFS/NTF 64 Novell Netware b7 BSDI fs         fc VMware VMKCORE
18 AST SmartSleep 65 Novell Netware b8 BSDI swap       fd Linux raid auto
1b Hidden W95 FAT3 70 DiskSecure Mult bb Boot Wizard hid fe LANstep
1c Hidden W95 FAT3 75 PC/IX           be Solaris boot    ff BBT

[root@localhost ~]# fdisk /dev/hda

The number of cylinders for this disk is set to 9733.
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): t(Press t for change ID)
Partition number (1-11): 9(type partition number )
Hex code (type L to list codes): fd(write fd for convert ID to RAID)
Changed system type of partition 9 to fd (Linux raid autodetect)

Command (m for help): t
Partition number (1-11): 10
Hex code (type L to list codes): fd
Changed system type of partition 10 to fd (Linux raid autodetect)

Command (m for help): t
Partition number (1-11): 11
Hex code (type L to list codes): fd
Changed system type of partition 11 to fd (Linux raid autodetect)

Command (m for help): w(Press w for save)
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.

[root@localhost ~]# fdisk -l(For show ID)
Disk /dev/hda: 80.0 GB, 80060424192 bytes
255 heads, 63 sectors/track, 9733 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id System
/dev/hda1   *           1        2764    22201798+   7 HPFS/NTFS
/dev/hda2            2765        9733    55978492+   5 Extended
/dev/hda5            2765        6602    30828703+   7 HPFS/NTFS
/dev/hda6            6603        8514    15358108+ 83 Linux
/dev/hda7            8515        8603      714861   82 Linux swap / Solaris
/dev/hda8            8604        8628      200781   83 Linux
/dev/hda9            8629        8690      497983+ fd Linux raid autodetect
/dev/hda10           8691        8752      497983+ fd Linux raid autodetect
/dev/hda11           8753        8814      497983+ fd Linux raid autodetect

[root@localhost ~]# yum install mdadm(For install mdadm package)

For RAID 5:

[root@localhost ~]# mdadm -C /dev/md0 -l 5 -n 3 /dev/hda{9,10,11}

For RAID 0 :

[root@localhost ~]# mdadm -C /dev/md1 -l 0 -n 2 /dev/hda{9,10}

For RAID 1 :

[root@localhost ~]# mdadm -C /dev/md2 -l 1 -n 2 /dev/hda{9,10}

mdadm: array /dev/md0 started.

[root@localhost ~]# mkfs.ext3 /dev/md0(For change file system)
mke2fs 1.39 (29-May-2006)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
124672 inodes, 248928 blocks
12446 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=255852544
8 block groups
32768 blocks per group, 32768 fragments per group
15584 inodes per group
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376

Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 32 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.
[root@localhost ~]# mkdir /raid5
[root@localhost ~]# mount /dev/md0 /raid5/
[root@localhost ~]# vim /etc/fstab

/dev/md0                /raid5                  ext3    defaults        0 0

[root@localhost ~]# mdadm -D /dev/md0(For Show RAID devices)
/dev/md0:
        Version : 0.90
  Creation Time : Mon Oct 24 00:03:36 2011
     Raid Level : raid5
     Array Size : 995712 (972.54 MiB 1019.61 MB)
  Used Dev Size : 497856 (486.27 MiB 509.80 MB)
   Raid Devices : 3
  Total Devices : 3
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Mon Oct 24 00:05:28 2011
          State : clean
 Active Devices : 3
Working Devices : 3
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 64K

           UUID : 58290efa:377bd1aa:c4e791dc:92062b3c
         Events : 0.6

    Number   Major   Minor   RaidDevice State
       0       3        9        0      active sync   /dev/hda9
       1       3       10        1      active sync   /dev/hda10
       2       3       11        2      active sync   /dev/hda11
[root@localhost ~]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 hda11[2] hda10[1] hda9[0]
      995712 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]

unused devices: <none>

Md Saiful Islam Chowdhury