Online tool link: Link: http://www.ecs.umass.edu/ece/koren/architecture/Raid/raidhome.html

http://www.ecs.umass.edu/ece/koren/architecture/Raid/raidiator.html

http://www.ecs.umass.edu/ece/koren/architecture/Raid/reliability_tool.html

D1. Tool for Storage Efficiency:

(i) Consider a disk array of 250 disks. Compile the storage efficiency of various RAID configurations, and conclude on which RAID configuration has the highest and lowest storage efficiency

(6 marks)

(ii) What is the main difference between RAID4 and RAID5? What problem does the RAID5 solve when compared to RAID4?

(4 marks)

D2. Tool for Reliability

Consider the following system with disks 1, 2 and 3.

-- 10 Disk 1s with 1,000,000-hour MTTF

-- 19 Disk 2s with 450,000-hour MTTF

-- 1 Disk 3s with 700,000-hour MTTF

-- MTTR for single disk is 8000 hours and 13,000 hours for the system

-- p (disk) is 1

-- Parity group size (G) is 30

(i) Determine MTTF of the system.

(2 marks)

(ii) Using the MTTF found above, compile the Reliability and MTTDL (in years) for RAID 5 and RAID6 configurations. Conclude on which RAID level is best for each failure characteristics?

	Reliability (years)		MTTDL (years)
	RAID5	P+Q	RAID5	P+Q
Double/Triple Disk Failure
System Crash + Disk Failure
Single/Double Disk Failure + Bit Error

(6 marks)

(iii) Derive the availability of a system based on its MTTF and MTTR.

(2 marks)