Mass-Storage Systems

Question 1

Random Access Time

Answer 1

The time it takes to move the disk arm to the desired cylinder.

Question 2

Seek Time

Answer 2

The time it takes for the desired sector to rotate under the disk read head.

Question 3

Storage Area Network (SAN)

Answer 3

Many hosts attached to many storage units; common in large storage environments.

Question 4

Bandwidth

Answer 4

(total number of bytes transferred) / (total time between first request and completion of last request)

Question 5

What are the sources of Disk I/O requests? (3)

Answer 5

1. Operating System
2. System Processes
3. User Processes

*The Operating System maintains the queue of requests per disk or device.

Question 6

What are the Disk Scheduling Algorithms? (5)

Answer 6

1. FCFS (first come first serve)
2. SSTF (shortest seek time first)
3. SCAN - arm starts reading at one end and services requests as it moves toward the other end, sweeping back and forth reversing direction.
4. CSCAN - similar to SCAN, but instead of reversing direction the arm proceeds back to its original position.
5. Look/CLOOK - arm only goes as far as the last request in either direction and reverses immediately.

Question 7

Low Level / Physical Formatting

Answer 7

Dividing a disk into sectors that the disk controller can read and write.

*usually 512 bytes of data per sector

Question 8

Partition

Answer 8

Dividing a disk into one or more cylinders, each treated as a logical disk.

Question 9

Logical Formatting

Answer 9

Making/implementing a file system.