Database Systems 6th Edition by Ramez Elmasri, Shamkant B. Navathe

تمرين 9

Consider a disk with the following characteristics (these are not parameters of any particular disk unit): block size B=512 bytes, interblock gap size G=128 bytes, number of blocks per track=20, number of tracks per surface=400. A disk pack consists of 15 double-sided disks.
(a) What is the total capacity of a track and what is its useful capacity (excluding interblock gaps)?
(b) How many cylinders are there?
(c) What is the total capacity and the useful capacity of a cylinder?
(d) What is the total capacity and the useful capacity of a disk pack?
(e) Suppose the disk drive rotates the disk pack at a speed of 2400 rpm (revolutions per minute); what is the transfer rate in bytes/msec and the block transfer time btt in msec? What is the average rotational delay rd in msec? What is the bulk transfer rate (see Appendix B)?
(f) Suppose the average seek time is 30 msec. How much time does it take (on the average) in msec to locate and transfer a single block given its block address?
(g) Calculate the average time it would take to transfer 20 random blocks and compare it with the time it would take to transfer 20 consecutive blocks using double buffering to save seek time and rotational delay.