5.1 Mass Storage System

magnetic disks

provide bulk of secondary storage of modern computers

transfer rate

_____ ______ is rate at which data flow between drive and computer

positioning time (random-access time)

is time to move disk arm to desired cylinder (seek time) and time for desired sector to rotate under the disk head (rotational latency)

head crash

results from disk head making contact with the disk surface

host controller

in computer uses bus to talk to disk controller built into drive or storage array

access latency

Average seek time + average latency

average i/o time

Average access time + (amount to transfer / transfer rate) + controller overhead

Disk bandwidth

The total number of bytes transferred, divided by the total time between the first request for service and the completion of the last transfer

logical blocks

The smallest unit of transfer, addressed as a large 1-dimensional array

Low-level formatting

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

network attached storage

is storage made available over a network rather than over a local connection (such as a bus)

shortest seek time first

selects the request with the minimum seek time from the current head position

scan

• Sometimes called the elevator algorithm

• the disk arm starts at one end of the disk, and moves toward the

  other end, servicing requests until it gets to the other end of the

  disk, where the head movement is reversed and servicing

  continues.

c-scan

• Provides a more uniform wait time than SCAN

• The head moves from one end of the disk to the other, servicing

requests as it goes

c-look

• a version of C-SCAN

• Arm only goes as far as the last request in each direction,

  then reverses direction immediately, without first going all

  the way to the end of the disk

clusters

To increase efficiency most file systems group blocks into _____

bootstrap loader

program stored in boot blocks of boot partition

sector sparing

Methods such as _____ _____ used to handle bad blocks

swap-space

virtual memory uses disk space as an extension of main memory

raid

redundant array of inexpensive disks

mirroring, shadowing

_____ or ______ keeps duplicate of each disk

snapshot

is a view of file system before a set of changes take place (i.e. at a point in time)