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Operating Systems: File Systems Flashcards

1
Q

What secondary storage technology still provides the bulk of modern computers’ storage?

A

Magnetic disks remain the primary secondary storage technology.

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2
Q

Which three key performance aspects of a disk drive are mentioned in the mass-storage structure overview?

A

Rotation rate

Transfer rate

Positioning time (the time required to move the arm to the desired location and rotate to the correct data)

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3
Q

What are two characteristics of solid-state devices (SSDs) as described?

A

They are non-volatile and much faster than magnetic disks

They have no moving parts and may have a shorter lifespan

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4
Q

For what purposes is magnetic tape typically used in mass storage?

A

Magnetic tape is used for backup, archive, and cold storage.

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5
Q

How can disks be attached to a computer according to the disk attachment overview?

A

Disks can be removable

They are attached via an I/O bus

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6
Q

Name at least three bus types used to connect disks to a computer.

A

EIDE or ATA

SATA

USB
Additional examples include Fibre Channel, SCSI, SAS, and Firewire.

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7
Q

What role does the host controller play in disk attachment?

A

The host controller communicates with the disk controller (which is built into the drive or storage array) via the bus.

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8
Q

How are disk drives logically addressed according to the disk structure slide?

A

They are addressed as large one-dimensional arrays of logical blocks.

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9
Q

What is a logical block in the context of disk storage?

A

A logical block is the smallest unit of transfer created by low-level formatting on physical media.

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10
Q

How are logical blocks typically mapped on magnetic disks?

A

They are mapped sequentially into sectors on the disk, with sector 0 being the first sector of the first track on the outermost cylinder.

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11
Q

What complications might arise in logical-to-physical addressing of disks?

A

Bad sectors may exist

The number of sectors per track may vary because of constant angular velocity

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12
Q

What components make up a storage array?

A

Controllers (including memory and controlling software, sometimes NVRAM)

Ports to connect hosts

A varying number of disks (from a few to thousands)

Features like RAID, hot spares, and hot swap capabilities

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13
Q

How do storage arrays contribute to overall storage efficiency?

A

By enabling shared storage and offering features such as RAID, they improve efficiency and may include functionalities (like snapshots or thin provisioning) that are also found in some file systems.

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14
Q

What is a Storage Area Network (SAN) and where is it commonly used?

A

A SAN is a high-speed network that provides remote storage access to multiple servers, commonly used in large storage environments.

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15
Q

How does a SAN differ from simple network-attached storage (NAS)?

A

SANs typically offer higher-speed data transfer and flexible, centralized storage for enterprise applications, while NAS focuses on file-level access over a network.

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16
Q

What is the primary responsibility of the operating system in disk scheduling?

A

The OS must schedule disk requests to maximize fast access time and disk bandwidth while minimizing the movement of physical parts.

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17
Q

Why is First-Come-First-Served (FCFS) not the most efficient disk scheduling method?

A

FCFS does not account for the physical movement required by disk drives and may result in longer seek times and lower overall performance.

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18
Q

What is Shortest Seek Time First (SSTF) in disk scheduling?

A

SSTF services the disk request that requires the shortest seek from the current head position, thereby reducing overall seek time.

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19
Q

How does the SCAN (elevator) disk scheduling algorithm operate?

A

The disk arm moves from one end of the disk to the other, servicing requests along the way, then reverses direction.

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20
Q

What distinguishes C-SCAN from SCAN disk scheduling?

A

C-SCAN scans only in one direction and, upon reaching the end, immediately jumps back to the beginning, offering more uniform wait times.

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21
Q

What additional disk scheduling algorithms are mentioned besides FCFS, SSTF, and SCAN/C-SCAN?

A

LOOK and C-LOOK are also mentioned; these algorithms only scan as far as the last request in the queue before reversing direction.

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22
Q

Why might an operating system choose one disk scheduling algorithm over another?

A

Performance depends on the number and types of requests and may be influenced by the file-allocation method; the algorithm should be modular to allow easy replacement if needed.

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23
Q

What are the two main tasks encompassed by OS disk management?

A

Managing low-level, physical formatting of disks

Handling logical disk management through partitioning and logical formatting

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24
Q

What does low-level (physical) formatting involve?

A

It divides the disk into sectors that the disk controller can read and write, where each sector typically contains:

Header information (metadata)

Data (usually 512 bytes or more)

Error Correction Codes (ECC) for error detection and correction
Low-level formatting is generally performed at the factory.

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25
How is a disk partitioned in logical disk management?
The disk is divided into logical disks (groups of cylinders), using schemes such as: MBR (Master Boot Record), which supports up to four primary partitions and is limited to 2TB disks GPT (GUID Partition Table), which supports larger disks and an unlimited number of partitions
26
What is low-level (physical) formatting in disk management?
It is the process of dividing the disk into sectors that the disk controller can read and write. This creates logical blocks on the physical media.
27
What components does each sector typically contain during low-level formatting?
Header information (metadata about the sector) Data (usually 512 bytes or more in modern drives) Error Correction Codes (ECC) for detecting and correcting errors
28
How often is low-level formatting performed and by whom?
It is typically performed at the factory and is rarely needed by end users.
29
What is the purpose of partitioning in logical disk management?
Partitioning structures the disk to store data efficiently by dividing it into logical disks (groups of cylinders).
30
Which partitioning schemes are mentioned and what are their key differences?
MBR (Master Boot Record): Supports up to four primary partitions and is limited to 2TB disks GPT (GUID Partition Table): Supports larger disks and an unlimited number of partitions
31
What is logical formatting (filesystem creation) and what does it accomplish?
After partitioning, logical formatting applies a filesystem to the disk, organizing storage into blocks (often grouped into clusters) to manage and store files efficiently.
32
Name some common filesystems used in logical formatting.
Examples include NTFS (Windows), ext4 (Linux), APFS (macOS), FAT32, and exFAT.
33
How do journaling filesystems improve reliability?
They track changes before committing them, which helps maintain consistency and recover from failures.
34
What is raw disk access?
It is when certain applications, such as databases or virtual machines, bypass the traditional filesystem and access disk blocks directly.
35
What are the benefits of raw disk access?
Performance optimization by avoiding filesystem overhead Custom block management that gives more control over data storage
36
What is the boot block and its role in the boot process?
The boot block contains essential code required to initiate the boot process. It is used by the bootstrap loader to start up the operating system.
37
What tasks does the bootstrap loader perform?
Locates and loads the OS bootloader from the disk Initializes system hardware Transfers control to the OS kernel
38
What is swap-space management and why is it important?
Swap-space management uses disk space as an extension of main memory, enabling the system to handle more processes than available RAM.
39
How can swap-space be implemented?
Swap file: A special file within the normal filesystem Dedicated swap partition: A separate disk partition optimized for swapping
40
What performance considerations are associated with swap-space management?
Using SSDs for swap improves speed compared to HDDs Overuse of swap (thrashing) can severely degrade system performance
41
What is a Storage Area Network (SAN) and where is it used?
A SAN is a high-speed network that provides remote storage access for multiple servers, commonly used in large storage environments.
42
What key advantages do SANs offer?
Centralized storage for better management and scalability High-speed data transfer compared to traditional NAS Support for enterprise applications such as databases and virtualization
43
What does RAID stand for, and what is its purpose?
RAID stands for Redundant Array of Independent Disks; it provides redundancy and performance improvements by combining multiple disk drives into a single logical unit.
44
Which common RAID levels are mentioned and what are their primary characteristics?
RAID 0 (Striping): Improves performance, but offers no redundancy RAID 1 (Mirroring): Duplicates data for redundancy RAID 5 (Striping with Parity): Balances performance and fault tolerance RAID 10 (1+0): Combines mirroring and striping for high performance and reliability
45
How can RAID be implemented in a system?
RAID can be implemented in hardware using dedicated RAID controllers or in software managed by the operating system.
46
What additional disk management services may the OS provide?
Encryption (e.g., BitLocker, LUKS) for security Snapshots to capture the state of the system at a given time Compression and deduplication to reduce storage space usage by eliminating redundant data
47
What role do files and filesystems play beyond low-level disk management?
They provide a high-level structure that facilitates data storage by organizing and managing files, enabling users and applications to interact with data efficiently.
48
How is a file defined in the context of file systems?
A file is a contiguous logical address space that can store data or programs. It may be structured, unstructured, or semi-structured and support sequential or random access.
49
What are the key attributes that define a file?
Name Identifier Type Location Size Protection Time, date, and user identification Extended attributes
50
What additional file attribute information is specifically mentioned for OS X?
OS X file attributes follow the general list (name, identifier, type, location, size, protection, timestamps, extended attributes) with system-specific metadata; no extra details are provided beyond the standard attributes.
51
Which operations must an operating system provide for file management?
Create Write (at the current write point) Read (from the current read point) Seek (reposition within a file) Delete Truncate Open (load into memory) Close (store changes to disk)
52
What data is tracked in the open-file table?
A pointer for each open file indicating the last read/write location (file pointer) per process File-open count to know when a file can be removed from the table Cached disk location information Per-process access rights
53
How does open file locking work in many operating systems?
It functions similarly to reader-writer locks Shared locks allow multiple processes to read concurrently Exclusive locks allow one process to write Can be either mandatory (access denied if locks conflict) or advisory (processes decide based on lock status)
54
What information is used to determine a file’s type by its extension?
Examples include: Executable files: typical extensions are exe, com, bin Object files: obj, o Multimedia files: mpeg, mov, mp3, mp4, avi Archive files: rar, zip, tar Printable/viewable files: gif, pdf, jpg Library files: lib, a, so, dll Word processor documents: docx Batch or script files: bat, sh Source code files: c, cc, java, perl, asm Additionally, “magic numbers” (the first few bytes) and known pattern databases help determine file type.
55
What does the file structure define in a file system?
It defines how data is organized, stored, and represented in a file. The OS uses an abstract layer for managing file data so that applications can interact with files efficiently and securely.
56
What types of file structures are mentioned?
None (a simple sequence of words or bytes) Simple record structures (lines, fixed-length records, variable-length records) Complex structures (formatted documents, relocatable load files) Additionally, complex structures can be simulated in an unstructured file by inserting appropriate control characters.
57
What are the primary methods of file access provided by the OS?
Sequential Access: reading or writing in order, one record after the other Direct Access: accessing specific blocks or records (often record-based), enabling random read or write operations Other methods, such as index-based access, can be built on top of direct access.
58
What purpose do directories serve in a file system?
Directories add structure by grouping file information in nodes, making it easier to manage, locate, and organize files.
59
How does the disk get structured before a file system is applied?
The disk is subdivided into partitions, which can be used raw (without a file system) or formatted with a file system Each partition with a file system is known as a volume The volume’s metadata is tracked in a device directory or volume table of contents Special-purpose file systems may exist alongside general-purpose ones
60
What are the main operations provided for directory management?
Searching for a file Creating a file Deleting a file Listing directory contents Renaming a file Traversing the file system
61
What features should a directory structure support?
Efficiency in locating files quickly Flexible naming so that different users can have files with the same name and the same file can have multiple names Logical grouping based on properties such as type, size, or creation/modification date
62
What is a single-level directory and what problem does it pose?
A single-level directory is a flat structure for all users, which leads to naming and grouping problems since all files reside in one common space.
63
How do tree-structured directories improve file management?
They allow efficient searching and grouping They support both absolute and relative path names (with . for current directory and .. for parent directory) They facilitate logical organization of files within nested subdirectories Unix systems also use ~ to refer to a user’s home directory
64
What are acyclic-graph directories and how do they differ from tree-structured directories?
Acyclic-graph directories allow multiple references (links) to the same file or subdirectory, avoiding duplication of data They use techniques such as backpointers, daisy-chain organization, or entry-hold counts (delete only when count reaches 0) They introduce a new directory entry type called a “link” that points to an existing file
65
What is the purpose of mounting a file system?
Mounting makes a file system accessible by attaching its contents at a designated mount point within the operating system’s directory structure. This is fundamental for making storage devices (local, external, or network) usable.
66
How are mount points typically represented in a file system?
Mount points are directories (for example, “/users/sue/jane” or “/prog/doc”) where the contents of the mounted file system become available to the user.
67
What does mounting a file system mean?
Mounting a file system means making its contents accessible at a designated location—called a mount point—within the operating system's directory structure.
68
Why is file system mounting fundamental for system usability?
Because mounting allows local disks, external drives, or network shares to be accessed in a standardized way, making storage devices usable within the OS.
69
What is a mount point?
A mount point is the specific directory within the operating system’s file hierarchy where the contents of a mounted file system become accessible.
70
What benefits does file sharing offer on multi-user systems?
It allows multiple users to access common files Facilitates collaboration Enables sharing of resources across distributed systems (e.g., via network file systems)
71
How are remote file systems accessed in a distributed environment?
Remote file systems are accessed using networking protocols; methods include: Manual access via FTP Seamless access using distributed file systems Semi-automatic access via the World Wide Web
72
Which client-server protocols are standard for remote file sharing on UNIX and Windows?
NFS (Network File System) is standard for UNIX CIFS (Common Internet File System) is standard for Windows Additionally, standard OS file calls are translated into remote calls.
73
How do distributed information systems support remote file access?
They use unified naming services (such as LDAP, DNS, NIS, and Active Directory) to manage and provide access information needed for remote computing.
74
What control should a file owner have over file protection?
A file owner should control: Who can access the file What operations can be performed (read, write, execute, append, delete, list)
75
What are the typical types of access rights for a file?
Typical access rights include: Read Write Execute Append Delete List
76
In Unix file access control, what are the three classes of users?
Owner (user) Group Public (others)
77
How are access permissions set for files in Unix systems?
Permissions are set using mode bits (for read, write, execute) for the owner, group, and public. For example, using commands like chgrp to change group ownership and chmod to set permissions (e.g., chmod 761 game).
78
What is the purpose of access lists and groups in Unix?
They allow administrators to define and manage access rights on a per-user and per-group basis, ensuring controlled file access in a multi-user environment.
79
What is Windows Access Control?
Windows Access Control manages file and resource permissions using Access Control Lists (ACLs), which specify which users or groups can perform particular operations on a file or folder.
80
How do Windows ACLs differ from Unix file permissions?
Windows ACLs are more granular and can include multiple user and group entries They support inheritance and can specify detailed permissions (such as modify, read, write, execute, delete) for each entry Windows uses a different security model with its own set of system-provided rights and privileges

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