1 / 51

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.

temira
Download Presentation

Chapter Goals

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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

  2. 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

  3. Systems Architecture, Fifth Edition

  4. 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

  5. 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

  6. Logical and PhysicalStorage 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

  7. Systems Architecture, Fifth Edition

  8. The file is subdivided into multiple records and each record is composed of multiple fields. Systems Architecture, Fifth Edition

  9. File Content and Type • 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

  10. File Types • 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

  11. Systems Architecture, Fifth Edition

  12. Systems Architecture, Fifth Edition

  13. Directory Content and Structure • Contain information about files and other directories, typically name, file type, location, size, ownership, access controls, and time stamps Systems Architecture, Fifth Edition

  14. Hierarchical Directory Structure • 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

  15. Active (working) directory Systems Architecture, Fifth Edition

  16. Graph Directory Structure • 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

  17. Systems Architecture, Fifth Edition

  18. Storage Allocation • Secondary storage devices • Large number of storage locations; low frequency of allocation changes • Divided into allocation units Systems Architecture, Fifth Edition

  19. Allocation Units • 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

  20. Allocation Unit Size • 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

  21. Storage Allocation Tables • 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

  22. Systems Architecture, Fifth Edition

  23. Free allocation units are assigned to a hidden system file called SysFree. Systems Architecture, Fifth Edition

  24. All of a file allocation’s units are “chained” together in sequential order by a series of pointers. Systems Architecture, Fifth Edition

  25. Blocking • Logical record grouping within physical records • Described by a numeric ratio of logical records to physical records (blocking factor) Systems Architecture, Fifth Edition

  26. Blocking factor = 4:3 Blocking factor = 2:3 Systems Architecture, Fifth Edition

  27. Buffering • 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

  28. Systems Architecture, Fifth Edition

  29. File Manipulation • 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

  30. File Open and Close Operations • 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

  31. Delete and Undelete Operations • 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

  32. Access Controls • 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

  33. File Migration, Backup, and Recovery • Provided by most FMSs to protect files against damage or loss Systems Architecture, Fifth Edition

  34. File Migration(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

  35. Original Copy that has been updated to reflect new data Systems Architecture, Fifth Edition

  36. File Backup • 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

  37. Transaction Logging • 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

  38. File Recovery • 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

  39. Fault Tolerance • Methods of securing file content against hardware failure • File backup • Recovery • Transaction logging • Mirroring • RAID (Redundant Array of Inexpensive Disks) Systems Architecture, Fifth Edition

  40. Mirroring • 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

  41. RAID • 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

  42. Systems Architecture, Fifth Edition

  43. Data striping: Each segment is written in parallel to a separate disk. Systems Architecture, Fifth Edition

  44. If the parity disk fails, the other disks still retain their original data bits. Systems Architecture, Fifth Edition

  45. RAID 10: Mirrors individual disks (RAID 1), then stripes data (RAID 0) across multiple mirrored pairs. Systems Architecture, Fifth Edition

  46. Storage Consolidation • 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

  47. Storage Consolidation Systems Architecture, Fifth Edition

  48. Systems Architecture, Fifth Edition

  49. Systems Architecture, Fifth Edition

More Related