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Topic 3 - File management (Part 2 & 3) - Coggle Diagram

- - - - Contiguous allocation require s that each file occupy a set of contiguous block on the disk
      - Disk address define a linear ordering on the disk. With this ordering , assuming that only one job is accessing the disk, accessing b+l after block b normally require no head movement
      - Accessing a file that has been allocated contiguously is easy - For sequential access, the file system remember the disk address of the last block referenced and when necessary read the next block
      - Accessing a file that has been allocated contiguously is easy.
        
        For sequential access, the file system remembers the disk address of the last block referenced and, when necessary, reads the next block
    - - Linked allocation solves contiguous allocation
      - With linked allocation, each file is a linked list of disk block; the disk block may be scattered anywhere on the disk.
      - The directed contains a pointer to the first and last block of the file. Each block contains a pointer to the next block.
      - Problem
        
        effectively only for sequential access files
        
        Disk is being used for pointer, rather than for information
        
        Reliability:- Files are linked together by pointer scattered all over the disk, and consider what would hap A bug in the operating-system software or a disk hardware failure might result in picking up the wrong pointer
      - A write to the file causes the free-space management system to find a free block, and this new block is written to and is linked to the end of the file.- To read a file, we simply read blocks by following the pointers from block to block. - There is no external fragmentation with linked allocation, and any free block on the free-space list can be used to satisfy a request.
    - - Linked allocation solves the external fragmentation and size declaration problem of contiguous allocation.
      - Brings all the pointer together into the index block
      - Logical view
- - - - Database save files kept in tape or other storage media. Often used till the point of failure. Referred to as an operating system backup.
      - Types of Physical Backups
        
        Data files, redo log files, control files, saved
        
        Backup using:
        
        Windows NT operating system
        
        Oracle database utilities
        
        "COLD" backuop
        
        "HOT" backup
        
        Situation:
        
        Cold backup restores to the last backup
        
        If system failure, then the backup data was lost
        
        Hot database is used to minimize data lost. Often takes up larger disk space in the storage media.
    - - Import/Export
        
        Create a backup copy of the database
        
        Used to recover to the last backup.
  - - - Hardware problems
      - Power surge or failures
      - Head crashes
      - Dirt
      - Extreme Temperatures
      - Vandalism
      - Protection through:
        
        Small-users
        
        Removing floppy disks
        
        Locking them in a drawer
        
        Multi-users
        
        Controlled access process:
        
        Protection
        
        Controlled access
        
        Limit type of file access
        
        1 more item...