CS345 12 - File Management

CS345 12 - File Management - CS 345 File Systems Chapter 12...

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CS 345 File Systems Chapter 12
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BYU CS 345 File Management 2 File Management How would you describe “File Management”? Field Basic element of data (name, date, etc.) Record Collection of related fields treated as a unit (employee record) May be of a fixed or variable size File Collection of similar records Treated as an entity by applications Usually referenced by a name Access controls usually at file level Database Collection of related data files Relationships are explicit Used by a number of applications
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BYU CS 345 File Management 3 Common Operations Name some common file management operations: Retrieve All – Get all the records Retrieve One – Get just one record Retrieve Next – Get the next record in a specified sequence (sorted order) Retrieve Previous – Get record before this record Insert One – Add a new record to the file, possibly in a specific position Delete One – Remove an existing record Update One – Get a record, change it in some way, then write it to the file Retrieve Few – Get a set of records, often ones that meet a specific criteria (students in CSC 345)
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BYU CS 345 File Management 4 File Management What are the objectives/requirements? Objectives Meet the data requirements of the user Guarantee valid data (except GIGO) Optimize performance - both throughput and response time Support a wide variety of devices Minimize lost or destroyed data Provide a standard set of I/O routines Provide support for multiple users Minimal Requirements: Create, delete, change files Control other’s access to files Restructure files as appropriate Able to move data between files Back up and recover files Reference files by a symbolic name
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BYU CS 345 File Management 5 Pile Se q Indx Has h File System Architecture What is the architecture of a file system? Device Drivers Communicate directly with device Basic File System Buffering, placing data on device Basic I/O Supervisor I/O initiation and termination Logical I/O – Deals with records Access method (sequential, hashed, …) Standard interface with the user Device Drivers Basic File System Basic I/O Supervisor Logical I/O
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BYU CS 345 File Management 6 File System Implementation Application Programs Devices I/O Control Device Drivers Interrupt Handlers input: get block 123 output: low-level inst. Basic File System Issue commands to appropriate driver get block 123 File Organization Module Files <--> Blocks Free Space Mgr. Logical File System Directory Protection Security
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BYU CS 345 File Management 7 File Management System What level of interaction does a user have with a file management system?
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