Ch. 12: Mass-Storage Systems
What is storage area network?
A private network connecting servers and storage units
In Host-Attached storage, disks can be attached to the computers directly via an ___
I/O Bus
_____ is rate at which data flow between drive and computer.
Transfer rate
____ is much more expensive than disk storage
main memory
What is seek time?
move disk to the target cylinder
Circular-SCAN is designed to ____
provide a more uniform wait time
positioning time is also called ___
random-access time
_____ is difficult for OS to calculate
rotational latency
Disk scheduling usually tries to minimize ____
seek time
Positioning time includes ____ and _____
seek time rotational latency
Tape is best for _____, ___ is much slower
sequential access random access
What does SSTF stand for?
shortest seek time first
Network-Attached Storage is ____
storage made available over a network instead of a local bus
What is rotational latency?
for the target sector to rotate under the disk head
Fiber Channel is ______
high-speed serial bus
Disks can be attached to the computer as:
host-attached storage network-attached storage storage area network
What is swap space?
disk space used by virtual memory as an extension of the main memory
What is Physical formatting
divide disk into sectors for controller to read/write
SCAN algorithm sometimes is called the ___
elevator algorithm
A _____ is likely to be more reliable than a ________
fixed disk removable disk or tape
Disk scheduling performance depends on the _____
# and types of requests
Which is the simplest scheduling algorithm?
FCFS
There are many disk scheduling algorithms: (5)
FCFS SSTF SCAN C-SCAN C-LOOK
______ provide bulk of secondary storage of computer system
Magnetic disks
____ is responsible for using hardware efficiently
OS
_____ is time to move disk arm to desired sector
Positioning time
___ and ____ moves head end to end, even no I/O in between
SCAN and C-SCAN
RAID can only detect/recover from ___
disk failures
What is Access latency?
amount of time needed to locate data
What is the average access time of a magnetic disk?
average seek time + average latency
Bandwidth is measured in ____
bytes per second
What is disk bandwidth?
the speed of data transfer, data/time data: total number of bytes transferred time: between the first request and completion of the last transfer
What are tertiary storage devices?
third level (after memory and magnetic disks) e.g. floppy disks, CD-ROMs, DVDs, usually removable, low cost
Disk Scheduling chooses ____
which pending disk request to service next
