Q. Illustrate Basic strategy used in RAID?

Basic strategy used in RAID is to replace large capacity disk drive with multiple smaller capacity disks. Data on these disks is distributed to allow concurrent access so improving overall input/output performance. It also provides an easy way of incrementing capacity of the disk. Please note that one of the major features of design is to compensate for increase in probability of failure of multiple disks by the use of parity information. Seven levels of RAID are given in Figure displayed above. Please note that levels 2 and 4 aren't commercially offered.

In RAID technologies have 2 significant performance considerations:

• Data Transfer Rate
• I/O Request rate

High data transfer rate depends on:

• Path between particular disks and Memory.
• Fulfilment of an I/O request by multiple disks of disk array. Therefore increasing the transfer rate.

I/O request rate is defined as time taken to fulfil an I/O request. This is a significant consideration while dealing with transaction processing systems such as Railway reservation system. A high I/O request rate can be acquired through distributing data requests on multiple disks.