RAID (Redundant Array of Independent Disks) connects multiple disks together to increase performance and reliability. It provides increased I/O throughput, data redundancy if a disk fails, and allows data to be restored. The main RAID levels are: RAID 0 uses disk striping for performance but no redundancy; RAID 1 uses mirroring for 100% redundancy; RAID 5 uses disk striping with parity data distributed across all disks. Higher RAID levels like RAID 6 provide even more fault tolerance. The best RAID level depends on performance and reliability needs.

1. RAID
 Redundant Array of Independent Disks
 Multiple secondary disks are connected
together to increase the performance, data
redundancy or both.

2. RAID
 Need:
 To increase the performance
 Increased reliability
 To give greater throughput
 Data are restored

3. RAID – Level 0

4. RAID – Level 0
 Data is broken down into blocks and these blocks are
stored across all the disks.
 Thus striped array of disks is implemented.
 There is no duplication of data in this level so once a
block is lost then there is no way recover it.
 It has good performance.

5. RAID – Level 1

6. RAID – Level 1
 uses mirroring techniques
 All data in the drive is duplicated to another
drive.
 It provides 100% redundancy in case of a
failure.
 Advantage: Fault Tolerance

7. RAID – Level 2

8. RAID – Level 2
 Use of mirroring as well as stores Error Correcting
codes for its data striped on different disks.
 Each data bit in a word is recorded on a separate disk
and ECC codes of the data words are stored on a
different set disks.
 Due to its complex structure and high cost, RAID 2 is
not commercially available.

9. RAID – Level 3

10. RAID – Level 3
 It consists of byte level stripping with dedicated
parity. In this level, the parity information is
stored for each disk section and written to
dedicated parity drive.
 Parity is a technique that checks whether data has
been lost or written over when it is moved from
one place in storage to another.

11. RAID – Level 3
 In the case of disk failure, the parity disk is
accessed and data is reconstructed from the
remaining devices.
 Once the failed disk is replaced, the missing
data can be restored on the new disk.

12. RAID – Level 4

13. RAID – Level 4
 It consists of block level stripping with a
parity disk.

14. RAID – Level 5

15. RAID – Level 5
 RAID 5 writes whole data blocks onto
different disks, but the parity bits generated for
data block stripe are distributed among all the
data disks rather than storing them on a
different dedicated disk.

16. RAID – Level 6

17. RAID – Level 6
 RAID 6 is a extension of Level 5.
 In this level, two independent parities are generated
and stored in distributed fashion among multiple disks.
 Two parities provide additional fault tolerance.
 This level requires at least four disk drives to
implement RAID.

18.  The factors to be taken into account in
choosing a RAID level are:
 Performance requirements in terms of number of
I/O operation.
 Performance when a disk has failed.
 Performance during rebuild.