Operating Systems for Programmers CHAPTER 9
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
