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Chapter Goals. Describe the components and functions of a file management system Compare the logical and physical organization of files and directories Explain how secondary storage locations are allocated to files and describe the data structures used to record those allocations.

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Chapter goals
Chapter Goals

  • Describe the components and functions of a file management system

  • Compare the logical and physical organization of files and directories

  • Explain how secondary storage locations are allocated to files and describe the data structures used to record those allocations

Systems Architecture, Fifth Edition


Chapter goals continued
Chapter Goals (continued)

  • Describe file manipulation operations, including open, close, read, delete, and undelete operations

  • List access controls that can be applied to files and directories

  • Describe security, backup, recovery, and fault tolerance methods and procedures

  • Compare and contrast storage area networks and network-attached storage

Systems Architecture, Fifth Edition



File management systems
File Management Systems

  • Collection of system software that manages all aspects of user and program access to secondary storage

  • Usually part of the operating system

  • Translates operations into commands to physical storage devices

  • Implemented in four layers (command layer, file control, storage I/O control, and secondary storage devices)

Systems Architecture, Fifth Edition


Bridges between logical and physical views of secondary storage

Allocates secondary storage locations to individual files and directories

Includes software modules for device drivers for each storage device or device controller, interrupt handlers, buffers and cache managers

Systems Architecture, Fifth Edition


Logical and physical storage views
Logical and Physical storageStorage Views

  • Logical view

    • Collection of files organized within directories and storage volumes

  • Physical view

    • Collection of physical storage locations organized as a linear address space

Systems Architecture, Fifth Edition



The file is subdivided into multiple records and each record is composed of multiple fields.

Systems Architecture, Fifth Edition


File content and type
File Content and Type record is composed of multiple fields.

  • FMS supports limited number of file types:

    • Executable programs

    • Operating system commands

    • Textual or unformatted binary data

  • Modern FMSs can define new file types and install utility programs to manipulate them (file association)

Systems Architecture, Fifth Edition


File types
File Types record is composed of multiple fields.

  • Normally declared when a file is created and:

    • Stored within a directory, or

    • Declared through a filename convention

  • Determine:

    • Physical organization of data items and data structures within secondary storage

    • Operations that may be performed upon the file

    • Filename restrictions

Systems Architecture, Fifth Edition


Systems Architecture, Fifth Edition record is composed of multiple fields.


Systems Architecture, Fifth Edition record is composed of multiple fields.


Directory content and structure
Directory Content and Structure record is composed of multiple fields.

  • Contain information about files and other directories, typically name, file type, location, size, ownership, access controls, and time stamps

Systems Architecture, Fifth Edition


Hierarchical directory structure
Hierarchical Directory Structure record is composed of multiple fields.

  • Directories can contain other directories, creating a tree structure, but cannot be contained within more than one parent

  • Ways that names of access paths can be specified:

    • Complete path (fully qualified reference)

    • Relative path

  • Each storage device has a root directory

Systems Architecture, Fifth Edition


Active (working) directory record is composed of multiple fields.

Systems Architecture, Fifth Edition


Graph directory structure
Graph Directory Structure record is composed of multiple fields.

  • More flexible than hierarchical directory structure

    • Files and subdirectories can be contained within multiple directories

    • Directory links can form a cycle

Systems Architecture, Fifth Edition


Systems Architecture, Fifth Edition record is composed of multiple fields.


Storage allocation
Storage Allocation record is composed of multiple fields.

  • Secondary storage devices

    • Large number of storage locations; low frequency of allocation changes

    • Divided into allocation units

Systems Architecture, Fifth Edition


Allocation units
Allocation Units record is composed of multiple fields.

  • Smallest number of secondary storage bytes that can be allocated to a file; cannot be smaller than unit of data transfer between storage device and controller (block)

  • Assigned/reclaimed by FMS as files and directories are created or expanded/shrink or are deleted

  • Size difficult to change once set

Systems Architecture, Fifth Edition


Allocation unit size
Allocation Unit Size record is composed of multiple fields.

  • Tradeoffs

    • Efficient use of secondary storage space for files

    • Size of storage allocation data structures

    • Efficiency of storage allocation procedures

  • Smaller units: More efficient use of storage space

  • Larger units: Allow smaller storage allocation data structures

Systems Architecture, Fifth Edition


Storage allocation tables
Storage Allocation Tables record is composed of multiple fields.

  • Data structures that record which allocation units are free and which belong to files

  • Format and content vary across FMSs

  • Can contain linked lists in simpler FMSs or indices or other complex data structures in more complex FMSs

Systems Architecture, Fifth Edition


Systems Architecture, Fifth Edition record is composed of multiple fields.


Free allocation units are assigned to a hidden system file called SysFree.

Systems Architecture, Fifth Edition


All of a file allocation’s units are “chained” together in sequential order by a series of pointers.

Systems Architecture, Fifth Edition


Blocking
Blocking together in sequential order by a series of pointers.

  • Logical record grouping within physical records

  • Described by a numeric ratio of logical records to physical records (blocking factor)

Systems Architecture, Fifth Edition


Blocking factor = 4:3 together in sequential order by a series of pointers.

Blocking factor = 2:3

Systems Architecture, Fifth Edition


Buffering
Buffering together in sequential order by a series of pointers.

  • Temporary storage of data as it moves between programs and secondary storage devices

    • Physical records are stored in the buffer as they are read from secondary storage

    • FMS extracts logical records from buffers and copies them to data area of the application program

  • Each buffer is the size of one allocation unit

  • Improves I/O performance if enough are used

Systems Architecture, Fifth Edition


Systems Architecture, Fifth Edition together in sequential order by a series of pointers.


File manipulation
File Manipulation together in sequential order by a series of pointers.

  • Exact set of service layer functions varies among FMSs, but typically includes create, copy, move, delete, read, and write

  • Application programs interact directly with FMS through OS service layer

  • Users interact indirectly with FMS through command layer

Systems Architecture, Fifth Edition


File open and close operations
File Open and Close Operations together in sequential order by a series of pointers.

  • File open

    • Causes FMS to find the file, verify access privileges, allocate buffers, and update internal table of open files

  • File close

    • Causes FMS to flush buffer content to the storage device, release buffers, update file time stamps, and update table of open files

Systems Architecture, Fifth Edition


Delete and undelete operations
Delete and Undelete Operations together in sequential order by a series of pointers.

  • Delete

    • Does not immediately remove files; some content remains on secondary storage unit all allocation units have been reassigned and overwritten

    • File content can be visible to intruders

  • Undelete

    • Can be used to reconstruct directory and storage allocation table contents

Systems Architecture, Fifth Edition


Access controls
Access Controls together in sequential order by a series of pointers.

  • Granted by file owners and system administrators for reading, writing, and executing files

  • Provide security at the expense of additional FMS overhead

Systems Architecture, Fifth Edition


File migration backup and recovery
File Migration, Backup, and Recovery together in sequential order by a series of pointers.

  • Provided by most FMSs to protect files against damage or loss

Systems Architecture, Fifth Edition


File migration version control
File Migration together in sequential order by a series of pointers.(Version Control)

  • Automatic storage and backup of old file versions

  • Balances storage cost of each file version with anticipated user demand for that version

Systems Architecture, Fifth Edition


Original together in sequential order by a series of pointers.

Copy that has been updated to reflect new data

Systems Architecture, Fifth Edition


File backup
File Backup together in sequential order by a series of pointers.

  • Protects against data loss (file content, directory content, and storage allocation tables)

  • Store backup copies on a different storage device in a different physical location

  • Manual or automatic

  • Full or incremental

Systems Architecture, Fifth Edition


Transaction logging
Transaction Logging together in sequential order by a series of pointers.

  • Automatically records all changes to file content and attributes in a separate storage area; also writes them to the file’s I/O buffer

  • Provides high degree of protection against data loss due to program or hardware failure

  • Imposes a performance penalty; used only when costs of data loss are high

Systems Architecture, Fifth Edition


File recovery
File Recovery together in sequential order by a series of pointers.

  • Automated and manual components

  • Can search backup logs for copies of lost or damaged files

  • Can perform consistency checking and repair procedures for crashed system or physically damaged storage device

Systems Architecture, Fifth Edition


Fault tolerance
Fault Tolerance together in sequential order by a series of pointers.

  • Methods of securing file content against hardware failure

    • File backup

    • Recovery

    • Transaction logging

    • Mirroring

    • RAID (Redundant Array of Inexpensive Disks)

Systems Architecture, Fifth Edition


Mirroring
Mirroring together in sequential order by a series of pointers.

  • All disk write operations are made concurrently to two different storage devices

  • Provides high degree of protection against data loss with no performance penalty if implemented in hardware

  • Disadvantages

    • Cost of redundant disk drives

    • Higher cost of disk controllers that implement mirroring

Systems Architecture, Fifth Edition


RAID together in sequential order by a series of pointers.

  • Disk storage technique that improves performance and fault tolerance

  • All levels except RAID 1 use data striping

    • Breaks a unit of data into smaller segments and stores them on multiple disks

  • Multiple levels can be layered to combine their best features (e.g. RAID 10)

  • Can be implemented in hardware or software

Systems Architecture, Fifth Edition


Systems Architecture, Fifth Edition together in sequential order by a series of pointers.


Data striping: together in sequential order by a series of pointers. Each segment is written in parallel to a separate disk.

Systems Architecture, Fifth Edition


If the parity disk fails, the other disks still retain their original data bits.

Systems Architecture, Fifth Edition


RAID 10: original data bits. Mirrors individual disks (RAID 1), then stripes data (RAID 0) across multiple mirrored pairs.

Systems Architecture, Fifth Edition


Storage consolidation
Storage Consolidation original data bits.

  • Overcomes inefficiencies of direct-attached storage (DAS) in multiple-server environments

  • Common approaches

    • Storage area network (SAN)

    • Network-attached storage (NAS)

Systems Architecture, Fifth Edition


Storage consolidation1
Storage Consolidation original data bits.

Systems Architecture, Fifth Edition




Summary
Summary original data bits.

  • File management systems

  • Directory content and structure

  • Storage allocation

  • File manipulation

  • Access controls

  • File migration, backup, and recovery

  • Storage consolidation

Systems Architecture, Fifth Edition


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