Chapter 11 - 17
As a general rule, an I/O system will return _______ of information about the status of the call.
1 bit
metaslabs
Chunks of blocks. In ZFS, a pool of storage is split into metaslabs for easier management.
SCAN Algorithm
Disk arm starts at one end of the disk and moves toward the other end servicing the request as it reaches each cylinder
Which of the following is not true as related to MS-DOS for FAT?
Each name maps to an inode number.
advanced configuration and power interface (ACPI)
Firmware common to pcs and servers that manages certain aspects of hardware including power and device information
Master File Directory (MFD)
IN two level directory implementation the index pointing to each UFD
What is the reason to design an operating system which recognizes the type of a file?
If an operating system knows what kind of file it is working with, it can then have a set of special operations that pretend to that type of file. So this could be like .exe, .sh and .com extensions that can be executed in binary to do something for a user or system. If the operating system doesn't know these files are binary executables then it will just output some garbage.
User-file directory (UFD)
In two level directory implementations, a per user directory of files
cluster
In windows storage a power of 2 number of disk sectors collected for I/O optimization
How does MS Windows API implement shared memory using memory-mapped files?
It first creates a file mapping for the file to be mapped and then establishing a view of the mapped file in a process virtual address space. A second process can then open and create a view of the mapped file in its virtual address space. The mapped file represents the shared-memory object that will enable communication to take place between the processes.
wear leveling
NVm selection of all of nand cells over time as write targets to avoid premature media failure due to subset failure
An advantage of SSDs over HDDs is
SSDs are faster and more reliable than HDDs
When considering a particular directory structure, we need to keep in mind the operations that are to be performed on a directory. List and briefly discuss those operations.
Search for a file - We need to be able to search a directory structure to find the entry for a particular file. Since files have symbolic names, and similar names may indicate a relationship among files, we may want to be able to find all files whose names match a particular pattern. Create a file - New files need to be created and added to the directory. Delete a file - When a file is no longer needed, we want to be able to remove it from the directory. List a directory - We need to be able to list the files in a directory and the contents of the directory entry for each file in the list. Rename a file - Because the name of a file represents its contents to its users, we must be able to change the name when the contents or use of the file changes. Traverse the file system: - We may wish to access every directory and every file within a directory structure.
random access time
Seek Time + rotation latency
free-behind
Sequential I/O perforamance optimization that removes a page or block from a buffer as soon as I/O to the next page is requested
Describe the main drawback of single-level directory structure.
Since all of the files are stored in a single directory, they all have to have unique file names like file1 file2 fileAgnsdkl!3o. The problem is that a user is not going to remember every file and might have difficulty finding one if it has a bunch of numbers after it because they needed a unique file name. It can become a problem in really large systems because the file names may need to be some sort of gibberish for it to be a unique name.
Flash Translation Layer (FTL)
Tables in nonvolatile memory based devices that track valid blocks
What is the advantage of C-SCAN over SCAN disk head scheduling?
The C-SCAN algorithm is a variant of SCAN algorithm. Like SCAN, C-SCAN moves the head from one end of the disk to the other, servicing requests along the way. When the head reaches the other end, however, it immediately returns to the beginning of the disk without servicing any requests on the return trip. This results in C-SCAN providing a more uniform wait time
What is the purpose of a UNIX mount table?
The UNIX mount table associates prefixes of pathnames with specific device names. To resolve a pathname, Unix looks up the name in the mount table to find the longest matching prefix; the corresponding entry gives the device name.
power collapse
The ability for applications to temporarily prevent the system from entering power collapse
What is constant angular velocity in relation to disk drives?
The disk head moves in and out above the disks so that it can read the memory there. The speed at which it reads something needs to be the same regardless if it is at the center of the disk or on the outer edge of the disk. If the rotation of the disk isn't going to change then the density of info on each track needs to increase towards the outer edge of the disk.
What are the factors influencing the selection of a disk-scheduling algorithm?
The locations of the memory block and how long it takes for the arm to move the head to those locations. Rotational latency can also affect the algorithm because the head will likely have to wait for the platter to rotate the desired sector to the head. Any operating system may be queueing requests for files such as priorities for some files request to be serviced first.
Copy semantics
The meaning assigned to data copying, whether a block writes from a process allows the data to be modified after the write has been requested.
What is the main disadvantage of having the operating system support multiple file structures?
The more file structures it supports the more code that has to be written to handle the types of files. This means that the more files that the system supports, the bigger the system has to be to store all the commands and operations to handle them. Also if a file that the operating system doesn't support but is applications require it in that structure, problems may occur.
Why is open() call implemented before a file is first used?
The open functions stops the operating system from needing to remember what file names are and have a whole process for evaluation these names. Instead open() is used to return a filehandle that is used for arguments in other calls. This open() call can also be used to set the file to a read-only or write-only file along with the ability to create a file.
What are the differences between per-process open-file table and a system-wide open-file table?
The per-process open-file table tracks all files that a process has open. Stored in this table is information regarding the process's use of the file. This could be if it is read or writing to the file and if it has access rights to the file. This table then points to the system-wide open-file table. The system-wide open-file table which holds process independent information such as the location of the file on disk, access dates, and file size. The system-wide open file table also holds what processes have specific files open.
double caching
The problem in which the same data might be in two different cahces; solved by a unified buffer cache
Which of the following statements regarding solid state disks (SSDs) is false?
They generally consume more power than traditional hard disks.
What are the three reasons that buffering is performed?
To cope with a speed mismatch between the producer of information to the consumer of that information. Another reason is to deal with a situation where one device can transfer 50 Mbps and the other can only transfer at 25 Mbps a buffer is used to make sure everything is transferred and that the previous device can go do something else. A third use is for buffering is to support copy semantics for application IO. This allows something to be copied from the buffer so that if the original location that the copy was gets changed, the copy in the buffer doesn't change. This buffer makes sure that what is being used was at the state of when the system call was put in and not what it is currently at.
band width
Total data transferred divided by total time between first service request last transfer completion
Some binary files can include a magic number. This mechanism is used by __________.
UNIX
spool
a buffer that holds output for a device such as a printer that cannot accept interleaved data steams
magic number
a crude method of storing a number at the start o a file to indicate the type of the data in the file
memory mapping
a file access method in which a file is mapped into the process memory space so that standard memory access instructions read and write the contents of the file; an alternative to the use of read() and write() calls
sequential access
a file access method in which contents are read in order from beginning to end
direct access
a file access method in which contents are read in random order or at least not sequentially
relative access
a file access method in which contents are read in random order or at least not sequentially
contiguous allocation
a file block allocation method in which all blocks of the file are allocated as a contiguous chunk of secondary storage
shell script
a file containing a set series to of commands (similar to a patch file) that are specific to the shell being used
advisory file lock mechanism
a file locking system in which the operating system does not enforce locking and files access leaving it to the processes to implement the details
access control list
a list of user names allowed to access a file
volume control block
a per volume storage block containing data describing the volume
Cylinder
a set of tracks at a given arm position
file-allocation table (fat)
a simple but effective method of disk space allocation used by MS-DOS. A section of storage at the beginning of each volume is set aside to contain the table which has one entry per block, is indexed by block number and contains the number of the next block in the file.
boot control block
a storage block of data containing information needed by the system to boot from the volume containing the block
Cache
a temporary copy of data stored in a reserved memory area to improve performance.
linked allocation
a type of file system block allocation in which each file is a linked list of allocated blocks containing the files contents.
terminal concentrator
a type of front end processor for terminals
asynchronous write
a write that is buffered and written i arbitrary order with the requesting thread continuing execution after the write is requested
Ram Drives
act like secondary storage but are created by device drivers
Head crash
an accident where the head damages the magnetic surface of the disk platter
component power management
an infrastructure that understands the relationship between components and whether each component is in use
device driver
an operating system component that provides uniform access to various devices and manages I/O to those devices
open-file table
an operation system data structure containing details of every file open within the system
UNIX systems considers each file to be a sequence of _______________
bit words, which length is defined by the users
The difference between a buffer and cache is
buffer holds only existing copy of the data and cache holds a copy of data that exists elsewhere
Which of the following is NOT a technique used for managing power consumption in mobile devices?
chilling with natural sources such as lake water, and solar panels.
Inode
contains information about the file, including ownership permissions and location of the file contents
What pointer is used for writing a file?
current-file-position pointer
close() operation _____ an open count associated with a given file.
decreases
indexed allocation
in file system block allocation combining all block pointers in one or more index blocks to address limits in linked allocation and allow direct access to each block
With _______ locking, once a process acquires an exclusive lock, the operating system will prevent any other process from accessing the locked file.
mandatory
Disk scheduling algorithms in operating systems consider only seek distances, because
modern disks do not disclose the physical location of logical blocks.
Which of the following related to I/O performance is not true?
network traffic cannot cause a high context-switch rate.
In the two-level directory, if a user refers to a particular file then__________________
only his/her own UFD (user file directory) is searched
When the exclusive lock is applied to a file then _____________
only one process can use this file
To prevent users from performing illegal I/O, we define all I/O instructions to be ______ instructions.
privileged
DRAMs are now commonly used for mass data storage, because
programs can share data easily when using RAMs.
Transfer Rate
rate at which data flow between the drive and the computer
The block number provided by the use to the operating system is normally a ____ block number.
relative
What are the two components of positioning time?
seek time + rotational latency
The simplest access method is
sequential
The SCAN scheduling algorithm ____.
services the request next to the current head position in the direction of the head movement
When the shared lock is applied to a file then ____________
several processes can acquire the lock concurrently
Over provisioning
space for data writes in non volatile memory devices the is not counted in the device free space
bit vector
string of n binary digits representing the status of n items
bitmap
string of n binary digits representing the status of n items
wakelocks
the ability for applications to temporarily prevent the system from entering power collapse
dynamic storage allocation
the class of file block allocation method that satisfy a request for n blocks from a list of free holes available
A relative path name defines a path from_________________________
the current directory
Because all file systems suffer from internal fragmentation, the following relation is true:
the larger block size, the greater the internal fragmentation
read point
the location in a file from which the next read will occur
Write pointer
the location in a file to which the next write will occur
tracks
the logical circular division of a platter.
extended file system
the most common class of linux file systems with ext3 and ext4 being the most commonly used file system types
compaction
the shuffling of storage to consolidate used space and leave one or more large holes available for more efficient allocation.
A current trend in I/O device technology and I/O subsystem is
there is an increasingly broad variety of I/O devices.
directory structure
used to organize the files
IBM's indexed sequential access method (ISAM)__________________________.
uses a small master index (kept in memory) that points to disk blocks of a secondary index, while the secondary index blocks point to the actual file blocks
synchronous writes
writes that are stored in the order in which they were issued are not buffered and have requesting threads wait for the writes to complete before continuing
Consider a disk queue holding requests to the following cylinders in the listed order: 116, 22, 3, 11, 75, 185, 100, 87. Using the SCAN scheduling algorithm, what is the order that the requests are serviced, assuming the disk head is at cylinder 88 and moving upward through the cylinders?
100 - 116 - 185 - 87 - 75 - 22 - 11 - 3
A two-level directory can be thought as a tree of height _________
2 and its root is MFD
Consider a disk queue holding requests to the following cylinders in the listed order: 210, 67, 11, 99, 87, 90, 19, 150. Using the C-SCAN scheduling algorithm, what is the order that the requests are serviced, assuming the disk head is at cylinder 88 and moving upward through the cylinders?
90 - 99 - 150 - 210 - 11 - 19 - 67 - 87
I/O channel
A dedicated, special-purpose CPU that offloads I/O work from main CPU.
What is the internal representation of a directory in tree-structured directory?
A directory contains a set of files or subdirectories. A directory is simply another file, but it is treated in a special way. All directories have the same internal format. One bit in each directory entry defines the entry as a file(0) or as a subdirectory (1) Special system calls are used to create and delete directories.
logic block
A large one dimension al array used by storage devices for addressing
buffer
A memory area that stores data being transferred
absolute path name
A path name starting at the topo of the file system hierarchy
relative block number
An index relative to the beginning of the file. The first relative block of the file is block 0, the next is block 1, and so on through the end of the file
What is a disadvantage of the FCFS scheduling algorithm?
Basically, the FCFS algorithm can have situations where it spends a lot more time traveling back and forth in a high-frequency zigzag pattern. This is an extreme case that might have the head spend more time traveling to locations on the disk than actually servicing requests. It does all this while skipping over requests because they are in a later part of the queue.
