Title: An Introduction to Disk Drive Modeling
Authors: Chris Ruemmler and John Wilkes
Journal: IEEE Computer, March 1994

Context:
	Disk drive models are important for studying overall I/O performance
	Paper presents an overview of modern disk functionality(SCSI) and describes one 
	disk drive model.
	
Characteristics of Modern Disk Drives:
	Disk drive contains 'mechanism' and 'controller'. 
	Mechanism:
		Recording Components:	
			Storage density - Linear recording density, Tracks per inch(TPI).		
			Rotation Speed. 
		Positioning Components:
			Appropriate head reaches the desired track quickly and stays there in
			face of external vibrations, shocks and disk flaws.
			Seeking: Speedup + Coast + Slowdown + Settle.
				Short seeks: speedup+slowdown(proportional to square root of distance.) + settle
				Long seeks: coast(proportional to distance) + settle.
			Track Following:
				Uses positioning information recorded on disk. Use buffering to read before confirming
				that you are in the right position.
			Zoning:	Adjacent Cylinders grouped into zones. Outer zones have more sectors/track.
			Track Skewing: To read adjacent tracks without incurring additional rotational delay.
			Sparing: Flawed sectors are remapped to other sectors.
			
	Disk Controller:
		mediates access to 'mechanism'. Runs the track-following system. Transfers data between client and disk
		drive and manages an embedded cache.
		The most important feature to model is the data-caching characteristics of the disk.
			Read Caching, Write Caching, Read-ahead.
			
Model:
	- Host I/O driver; the CPU costs for executing it and its queuing strategy
	- SCSI bus including contention effects
	- Disk Controller effects: fixed controller overhead, SCSI bus disconnects during mechanism delays
	- Disk buffer Cache: Read-ahead, Write-behind(immediate reporting), and producer-consumer interlocks between
			mechanism and bus transfers
	- Data Layout model: Reserved Sparing areas, zoning, and track and cylinder skew.
	- Head movement effects: Seek time curve, settle time, head-switch time and rotation latency.