1. Chapter 12 File Management Systems

2. Outline Functions and components Storage allocation File manipulation
Access controls
Migration, backup, recovery

3. File Management Systems
Logical and Physical Storage Views
File Content and Type

4. File Management Systems
A File Management System (FMS) is implement in layers:
Command layer or application program
File control
Storage I/O control
Storage devices

6. File Management Systems
Storage devices – interact with the bus and with operating system device drivers to transfer data between storage devices and memory.
Storage I/O control – accesses storage locations and manages data movement between storage devices and memory.

7. File Management Systems
File Control – provides a set of service functions for manipulating files and directories.
Command layer or application program – users perform common file management functions such as copying, moving and renaming.

8. File Management Systems
Logical and Physical Storage Views
Logical Storage Views – viewed by users are a collection of files organized within directories and storage volumes.
Physical Storage Views – a collection of physical storage locations organized as a linear address space.

9. File Management Systems

10. Records and Fields

11. File Management Systems
File Content and Type
A file can store many different data types including text, numbers, complex data structures, and executable instructions.
Modern file management systems provide a framework to support additional file types.

12. File Management Systems
File Content and Type
File type normally is declared when a file is created.
In the UNIX file management system, the file type is stored within the directory. In the Windows file management system, the file type is declared through the extension.

13. File Management Systems

15. Directory Content and Structure
Hierarchical Directory Structure
Graph Directory Structure

16. Directory Content and Structure
Hierarchical Directory Structure
A directory contains information about files and other directories.
Typical directory contents include:
Name Size Time stamp
File Type Ownership
Location Access controls

17. Directory Content and Structure
Typical file ownership permissions are:
List
Read
Modify
Change

18. Directory Content and Structure
Time stamps include:
When the file was created
When the file most recently was read
When the file most recently was written
When the file last was backed up

19. Directory Content and Structure

20. Directory Content and Structure
Hierarchical Directory Structure
Directories can contain other directories.
Directories can not have more than one parent.
Sometimes called a tree structure.

21. Directory Content and Structure

22. Directory Content and Structure
Example: Traversing directories in the Windows command shell

23. Directory Content and Structure
Graph Directory Structure
Files and subdirectories can be contained within multiple directories.
Directory links can form a cycle.

24. Directory Content and Structure

25. Paths Where do operating systems look for executable files?
In the current directory
In the path
If directories are missing or in the wrong order, OS can’t find the right files
Example: Windows PATH

26. Paths and Environment Variables
Some programs use environment variables to store path information
If directories are missing or in the wrong order, programs can’t find the right files
Example: Java and the CLASSPATH

27. Paths, INI Files, Programs …
Paths are all over the place!
They are in initialization files, programs, the Windows registry, …
You need to be comfortable with absolute and relative file specs.

28. Outline Functions and components Storage allocation File manipulation
Access controls
Migration, backup, recovery

29. Storage Allocation Allocation Units Storage Allocation Tables
Blocking and Buffering

30. Storage Allocation Allocation Units
An allocation unit is the smallest number of secondary storage bytes that can be allocated to a file.
Allocation units can not be smaller than the unit of data transfer between the storage device and controller, which is normally called a block.

31. Storage Allocation Allocation unit size is usually a tradeoff among:
Systems Architecture
Chapter 12
Storage Allocation
Allocation unit size is usually a tradeoff among:
Efficient use of secondary storage space for files.
Size of storage allocation data structures.
Efficiency of storage allocation procedures.

32. Storage Allocation Storage Allocation Tables
Systems Architecture
Chapter 12
Storage Allocation
Storage Allocation Tables
A storage allocation table is a data structure that records which allocation units are free and which belong to files.

33. Systems Architecture
Chapter 12
Storage Allocation

34. Outline Functions and components Storage allocation File manipulation
Migration, backup, recovery
Access controls
Directories

35. Storage Allocation

36. Storage Allocation

37. Storage Allocation Blocking and Buffering
A logical record is a collection of data items, or fields, that is accessed by an application program as a single unit.
A physical record is the unit of storage transferred between the device controller and memory in a single operation.

38. Storage Allocation Blocking and Buffering
Logical record grouping within physical records is called blocking.
If a physical record contains just one logical record, then the file is said to be unblocked.

39. Storage Allocation

40. Storage Allocation Blocking and Buffering:
A FMS uses buffers in primary storage to store data temporarily as it moves between programs and secondary storage devices.
A buffer is a scratchpad for extracting logical records from physical records.

41. Storage Allocation

42. Outline Functions and components Storage allocation File manipulation
Access controls
Migration, backup, recovery

43. File Manipulation File Open and Close Operations
Delete and Undelete Operations

44. File Manipulation File Open and Close Operations
The FMS must perform several tasks, collectively called a file open operation, before an application program can read or write a file’s contents.

45. File Manipulation File Open Operation:
Locates the file within the directory structure and reads its directory entry.
Searches an internal table of open files to see if the file already is open.
Ensures that process has sufficient privileges to access the files.
Allocates one or more buffers.
Updates an internal table of open files.

46. File Manipulation File Close Operation:
Flushing the program’s file I/O buffers to secondary storage.
Deallocating buffer memory.
Updating the file’s directory entry time stamps.
Updating the open file table.

47. File Manipulation Delete and Undelete Operations
In most file management systems, files are not removed immediately from secondary storage when they are deleted.
The file’s storage allocation units are marked as free and its directory entry is marked as unused.
A user might be able to use the undelete operation to recover the file.

48. Access Controls
A File Management System helps prevent loss, corruption and unauthorized access to files.
The operating system is used to identify and authenticate users and their processes.
The file access is authenticated through id’s and passwords.

49. Outline Functions and components Storage allocation File manipulation
Access controls
Migration, backup, recovery

50. Access Controls For Example: UNIX defines three access control types:
Read
Write
Execute

51. Technology Focus – Windows NTFS

52. Outline Functions and components Storage allocation File manipulation
Access controls
Migration, backup, recovery

53. File Migration, Backup and Recovery
File Backup
Transaction Logging
File Recovery
Fault Tolerance
Mirroring

54. File Migration, Backup and Recovery
File Migration – management technique for secondary storage in which older versions of a file are moved automatically to less costly storage media or devices such as magnetic tape.

55. File Migration, Backup and Recovery

56. File Migration, Backup and Recovery
File Backup:
Full Backup
Incremental Backup
Differential Backup

57. File Migration, Backup and Recovery
Full Backup – the FMS copies all files and directories for an entire storage volume.
Incremental Backup – only the files that have been modified are archived.
Differential Backup – only the changed portions of the files are archived.

58. File Migration, Backup and Recovery
Transaction Logging
A form of automated file backup.
A transaction is any single change to file contents or attributes.
Transaction logging provides a high degree of protection against data loss due to program or hardware failure.

59. File Migration, Backup and Recovery
File Recovery
The file management system maintains backup logs to aid in locating backup copies of lost or damages files.
The recovery utility reconstructs as much of the directory and storage allocation data structures as possible and makes a consistency check.

60. File Migration, Backup and Recovery
Fault Tolerance
Describes methods of securing file content against hardware failure.
File backup, recovery, and transaction logging are forms or protection against disk failure.

61. File Migration, Backup and Recovery
Mirroring
A fault tolerance technique in which all disk write operations are made simultaneously or concurrently to two different storage devices.
Disk mirroring provides a high degree of protection against data loss with no performance penalty if implemented in hardware.

62. Technology Focus

63. Technology Focus

64. Technology Focus

65. Summary
The file management system (FMS), usually a part of the operating system, manages all aspects of user and program access to secondary storage.
With directories, users can organize the thousands of files stored in a typical computer system.

66. Summary
Secondary storage units are divided into allocation units, which are typically a few kilobytes in size.
The FMS allocates buffers to support program file I/O.

67. Summary
The FMS enforces access controls when accessing files on behalf of a user or program.
FMSs provide utilities to make backup copies of files and directories and to recover them if needed.