Raid and its levels

1. RAID TECHNOLOGY Patel Parth R(13MCA47)
Aman Sadhwani(13MCA50)

2. WHAT IS RAID?
RAID – Redundant Array of Independent Disks
RAID is a data storage virtualization technology that combines
multiple disk drive components into a logical unit for the
purposes of data redundancy or performance improvement.

3. MOTIVATION FOR RAID
•Just as additional memory in form of cache, can improve system
performance, in the same way additional disks can also improve
system performance
•In RAID, we use an array of disks. These disks operate independently
•Since there are many disks, multiple I/O requests can be handled in
parallel if the data required is on separate disks
•A single I/O operation can be handled in parallel if the data required
is distributed across multiple disks

4. WHY RAID?
Disk performance
Disk redundancy
Provide data security
Protects Data from disk failure

5. LEVELS OF RAID
There are 6 levels RAID schemes. These are called RAID 0, RAID 1, …
RAID 5
The common characteristic in all these levels is:
 A set of physical disk drives.
 The operating system views these separate disks as a single logical disk.
 Data is distributed across the physical drives of the array.
 Redundant disk capacity is used to store parity information.
 Parity information can help in recovering data in case of disk failure

6. RAID LEVEL 0
RAID 0 splits data evenly across two or more disks without parity
information and with speed as the intended goal.
RAID 0 is normally used to increase performance.
No parity checking of data in RAID 0.
RAID 0 implementation requires minimum 2 disks

7. RAID LEVEL 0

8. RAID LEVEL 0
Advantages
Increase speed
Easy implementation
No parity calculation
Disadvantages
No error checking of data

9. RAID LEVEL 1
This level is called "mirroring" as it copies data onto two disk drives
simultaneously.
As same data is placed on multiple disks, it is also called “data
mirroring”
Thus every disk in the array has a mirror disk that contains the same
data
Data can be read from either disk but is written on both disks

10. RAID LEVEL 1
Advantages
Main advantage is RAID 1 provides fault tolerance. If one disk fails,
the other automatically takes over.
So continuous operation is maintained.
RAID 1 is used to store systems software (such as drivers, operating
systems, compilers, etc) and other highly critical files.
Disadvantages
Main disadvantage is cost. Since data is duplicated, storage costs
increase.

11. RAID LEVEL 2
RAID 2 stripes data at the bit (rather than block) level, and uses a
Hamming code for error correction.
All hard disks eventually implemented Hamming code error
correction. This made RAID 2 error correction redundant and
unnecessarily complex

12. RAID LEVEL 3
Data is divided into byte units and written across multiple disk
drives.
Parity information is stored for each disk section and written to a
dedicated parity drive.
All disks can be accessed in parallel
Data can be transferred in bulk. Thus high speed data transmission is
possible

13. RAID LEVEL 3
In case of drive failure, the parity drive is accessed and data is
reconstructed from the remaining devices.
Once the failed drive is replaced, the missing data can be restored on
the new drive
RAID 3 can provide very high data transfer rates

14. RAID LEVEL 3

15. RAID LEVEL 4
RAID 4 is very similar to RAID 3 in that a parity disk drive is always
one of the five associated disk drives. But the difference is instead of
doing the parity at the byte level, in RAID 4, the parity is done at the
block level.

16. RAID LEVEL 5
RAID 5 consists of block-level striping with distributed parity.
Unlike in RAID 4, parity information is distributed among the drives.
It requires that all drives but one be present to operate at that block.

17. BENEFITS OF RAID
•Data loss can be very dangerous for an organization
•RAID technology prevents data loss due to disk failure
•RAID technology can be implemented in hardware or software
•Servers make use of RAID technology

18. THANK YOU 