Operating Systems for Programmers CHAPTER 9

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Hard error

result in lost data

shortest-seek-time-first algorithm

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

logical blocks

smallest unit of transfer

host controller

the controller at the computer end of the bus

Sector Sparing (Forwarding)

the controller can be told to replace each bad sector logically with one of the spare sectors

constant angular velocity (CAV)

the density of bits decreases from inner tracks to outer tracks to keep the data rate constant

Constant linear velocity (CLV)

the density of bits per track is uniform, speed changes

transfer rate

the rate at which data flow between the drive and the computer

mean time to repair

the time it takes (on average) to replace a failed disk and to restore the data on it

rotational latency

the time necessary for the desired sector to rotate to the disk head

seek time

the time necessary to move the disk arm to the desired cylinder

disk bandwidth

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

Swap space management

A _______ is a low-level task in the operating system. virtual memory uses disk space as an extension of main memory

sector slipping

As an alternative to sector sparing, some controllers can be instructed to replace a bad block by moving blocks down a spot

bad blocks

The areas of a storage medium unable to store data properly.

master boot record (MBR)

The first sector on a hard drive, which contains the partition table and a program the BIOS uses to boot an OS from the drive.

storage-area network (SAN)

a private network connecting servers and storage units

snapshot

a view of the file system before the last update took place

swap map

an array of integer counters, each corresponding to a page slot in the swap area

block-level striping

blocks of a file are striped across multiple disks

disk controller

consists of a special-purpose chip and electronic circuits that control the transfer of data, instructions, and information from a disk to and from the system bus and other components in the computer

data striping

consists of splitting the bits of each byte across multiple disks; such striping is called bit-level striping.

boot partition

contains the operating system and device drivers

SCAN algorithm (elevator algorithm)

disk arm starts at one end of the disk and moves toward the other end

Replication

involves the automatic duplication of writes between separate sites for redundancy and disaster recovery

solid-state disks (SSD)

nonvolatile memory that is used like a hard drive

hot spare

not used for data but is configured to be used as a replacement in case of disk failure

head crash

occurs when a read/write head touches the surface of a platter

LOOK Scheduling/ C-LOOK scheduling

LOOK for a request before continuing to move in a given direction

inode

a data structure for storing file system metadata

Nonvolatile RAM (NVRAM)

memory chips that do not lose their contents when the power to the computer is turned off

page slots

used to hold swapped pages (4-KB in size)

Circular SCAN (C-SCAN) scheduling

variant of SCAN to provide a more uniform wait time. when head reaches end of disk it returns to the original position at the start of the head


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