RAID

RAID (Redundant arrays of Inexpensive or Independent Disks):

RAID (Redundant arrays of Inexpensive or Independent Disks) Reliability Arrays are divided into reliability groups Each group has check disks How to evaluate Reliability Overhead Cost Useable Storage Capacity Percentage Performance

Different Levels of RAID:

Different Levels of RAID RAID Level 0 RAID Level 1 RAID Level 2 RAID Level 3 RAID Level 4 RAID Level 5 and others

RAID Level 0:

RAID Level 0

RAID Level 0:

RAID Level 0 RAID level 0 refers to disk arrays with stripping at the level of blocks, but without any redundancy such as mirroring or parity.

RAID Level 1 (Mirroring):

RAID Level 1 (Mirroring)

RAID Level 1:

RAID Level 1 Data duplicated, also the controller card Requires only two drives to implement Advantages Random Read performance=better than single disk Sequential Read Performance=fair, just as single disks Sequential Write Performance=good Random Write Performance=same as single disks Simple to Implement Disadvantage - high check disk overhead!

RAID Level 2:

RAID Level 2

RAID Level 2:

RAID Level 2 Uses Bit-level striping with Hamming codes for ECC Number of disks required depends on exact implementation Only fair fault tolerance Advantages Random Read performance=fair Sequential Read Performance=very good Sequential Write performance=good Disadvantages Random Write Performance=poor Requires a complex controller High overhead for check disks Not used in modern systems

RAID Level 3:

RAID Level 3

RAID Level 3:

RAID Level 3 Uses byte-level striping with dedicated parity Requires minimum three drives to implement Has good fault-tolerance Advantages Random Read Performance=good Sequential Read performance=very good Sequential Write performance=fair to good Lowest overhead for check disks Disadvantages Random Write performance=poor Complex controller design

RAID Level 4:

RAID Level 4

RAID Level 4:

RAID Level 4 Uses Block-level striping with dedicated parity Requires minimum of 3 drives to implement Has good fault-tolerance Advantages Random Read Performance=very good Sequential Read and Write performance=good Lowest overhead of check disks Disadvantages Quite complex controller design Random write performance=poor Not commonly used

RAID Level 5:

RAID Level 5

RAID Level 5:

RAID Level 5 Uses Block-level striping with distributed parity Requires a minimum of 3 drives to implement Advantages Random Read performance=very good Random Write performance=fair Sequential Read and Write performance=good Lowest overhead of check disks Disadvantages Most complex controller design Difficult to rebuild in the event of a disk failure

RAID Level 6:

RAID Level 6 Raid Level 6 uses Block-level striping with dual distributed parity

RAID Level 8:

RAID Level 8 Uses Mirroring and striping without parity

RAID Level 0+1:

RAID Level 0+1 Uses Mirroring and striping without Parity

RAID Level 53:

RAID Level 53 Uses Byte Striping with dedicated parity combined using block striping