Module 8 - File Systems

Flashcards generated from lecture notes on Operating Systems, focusing on file systems and storage management.

Mass Storage

Disk drives are the major secondary-storage I/O devices on most computers.

Disk Scheduling Algorithms

Disk scheduling algorithms can improve the effective bandwidth, the average response time, and the variance in response time.

RAID Algorithms

Disks are frequently made redundant via RAID algorithms for the amount of storage required on large systems.

Tertiary Storage

Tertiary storage is built from disk and tape drives that use removable media.

File System

Layer of OS that transforms blocks of disks into Files and Directories.

Disk Management

Collecting disk blocks into files.

Naming

Interface to find files by name, not by blocks.

Protection

Layers to keep data secure.

Reliability/Durability

Keeping of files durable despite crashes, media failures, attacks, etc.

User’s view of a File

Durable Data Structures.

System’s view (system call interface) of a File

Collection of Bytes.

System’s view (inside OS) of a File

Collection of blocks (a block is a logical transfer unit, while a sector is the physical transfer unit).

File Attribute: Name

Only information kept in human-readable form.

File Attribute: Type

Needed for systems that support different types of files.

File Attribute: Location

Pointer to file location on device.

File Attribute: Size

Current file size.

File Attribute: Protection

Controls who can do reading, writing, executing.

File Attribute: Time, date, and user identification

Data for protection, security, and usage monitoring.

Sequential Access

Bytes read in order.

Random Access (Direct)

Read/write element out of middle of array.

Content-Based Access

Find me 100 bytes starting with KUBI.

Directory Structure

A collection of nodes containing information about all files.

Entries in a device directory or volume table of contents

Record name, location, size, and type.

Efficiency in Directory Organization

Locating a file quickly.

Naming in Directory Organization

Convenient to users.

Grouping in Directory Organization

Logical grouping of files by properties.

Single-Level Directory

A single directory for all users.

Two-Level Directory

Separate directory for each user.

Tree-Structured Directories

Efficient searching and grouping capability.

Acyclic-Graph Directories

Have shared subdirectories and files.

Garbage collection in General Graph Directory

Determine when the last reference has been deleted and the disk space can be reallocated.

File System Mounting

Attach the file system at the specified mount point, which is typically an empty directory.

File Sharing

Sharing of files through protection schemes like owner and group.

Solution for Safe from physical damage (reliability)

Duplicate copies of files.

Solution for Improper access (protection)

Ability to access files, controlled by the file owner/creator.

Types of Access

Read, Write, Execute, Append, Delete, List.

File-System Structure

File structure, logical storage unit, collection of related information residing on secondary storage.

File control block

Storage structure consisting of information about a file.

Boot control block

Contains information needed by the system to book an operating from that partition.

Partition control block

Contain partition details, such as the number of blocks, size of the blocks, free-block/FCB count, and pointers.

In-Memory File System Structures

An in-memory partition table, directory structure, system-wide open-file table, and per-process open-file table.

Virtual File Systems (VFS)

Provides an object-oriented way of implementing file systems, allowing the same system call interface for different types of file systems.

Linear list of file names

Simple to program but time-consuming to execute.

Hash Table

Decreases directory search time, but with considerations for collisions and fixed size.

Allocation Methods

Contiguous, linked, and indexed allocation.

Contiguous Allocation

Each file occupies a set of contiguous blocks on the disk.

Linked Allocation

Each file is a linked list of disk blocks scattered anywhere on the disk.

File Allocation Table (FAT)

Directory entry contains the block number of the first block of the file.

Indexed Allocation

All pointers are brought together into the index block to solve fragmentation and size-declaration problems.

Indexed Allocation - Mapping

Mapping ensures access to files exceeding index table size using linked scheme or multilevel index.

Combined scheme

First 13 pointers kept within the file's inode (header) - direct, single indirect, double indirect, triple indirect

Counting

Keeping a pointer to the first free block and the number n of free contiguous blocks that follow the first block.

Free-behind and read-ahead

Techniques to optimize sequential access.

Disk cache

Section of main memory for frequently used blocks.

Page Cache

caches pages rather than file-system-oriented blocks using virtual memory techniques

Unified Buffer Cache

Uses the same page cache to cache both memory-mapped pages and ordinary file system I/O.

Consistency checking

Compares data in directory structure with data blocks on disk, and tries to fix inconsistencies.

Log Structured File Systems

Records each update to the file system as a transaction, written to a log.