Disk requests come in to disk driver for cylinders 10, 22, 20, 2, 40, 6, and 38, in that order. A seek takes 6 mes per cylinder moved. How much seek time is required for
(a) First-come, first served.
(b) Closest cylinder next.
(c) Elevator algorithm (initially moving upward).
In all cases, the arm is initially at cylinder 20.
A slight change of the elevator algorithm for scheduling disk requests is to always scan in the similar direction, In what respect is this modified algorithm better than elevator algorithm?
A RAID could fail if two or more of its drives crash within the short time interval. Assume that probability of one drive crashing in a given hour is p. What is the probability of a k-drive RAID failing in a given hour?
Consider magnetic disk consisting of 16 heads and 400 cylinders. This disk is divided into four 100-cylinder zones with the cylinders in different zones containing 160, 200, 240, and 280 sectors, respectively. Suppose that each sector contains 512 bytes, average seek time between adjacent cylinders is 1 msec, and disk rotates at 7200 RPM. Compute the (a) disk capacity, (b) optimal track skew, and (c) maximum data transfer rate.
Some operating systems give a system call rename to give a file a new name. Is there any difference at all between using this call to rename a file and just copying the file to a new file with the new name, followed by deleting the old one?
One way to use contiguous allocation of the disk and not suffer from holes is to compact disk every time a file is removed. As all files are contiguous, copying a file needs a seek and rotational delay to read file, followed by transfer at full speed. Writing file back needs the same work. Suppose a seek time of 5 msec, a rotational delay of 4 msec, a transfer rate of 8 MB/sec, and average file size of 8 KB, (a) how long does it take to read a file into main memory then prepare it back to disk at new location? (b) Using these numbers, how long will it take to compact half of a 16-GB disk? (c) Dose compacting the disk ever make any sense?
Free disk space could be kept track of using a free list or a bit map. Disk addresses need D bits. For a disk with B blocks, F of which are free, state condition under which free list uses less space than bitmap. For D having value 16 bits, express your answer as a percentage of the disk space that should be free.
What will happen if the bitmap or free list containing information about free disk blocks was totally lost due to a crash? Is there any way to recover from this disaster, or is it bye-bye disk? Discuss your answers for a UNIX and the FAT-16 file system separately.