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File-System implementation (NFS (overview (NFS views a set of…

- - - - Made in blocks
    - - File system
        
        provides efficeint and convenient access to disk and data
        
        Basic file system
        
        Needs only to issue generic commands to the debice driver
        
        Logical file sustem
        
        manages metadata information
        
        File control block
        
        FCB
      - I/O control
        
        Device drivers and interrupt handlers
        
        Move information from memory to disk system
      - File organization module
        
        information about files and logical blocks
- - - - Boot control block
        
        Information needed to boot the system
      - Volume control block
        
        Per volume
        
        volume details
      - Directory structure
        
        per file
      - FCB
        
        per file
        
        details about file
    - - mount table
        
        mounted volumes
      - directory-structure
      - system-wide open-file table
      - per-process open-file table
      - buffers file-system blocks being read
  - - - no file system
    - - Contains file system
    - - boot partition
        
        boot loader
        
        dual-bootable systems
    - - contains OS kernel and system fules
  - - - file-system-generic operations are spearted from implementation.
      - mechanism for representing a file through a network.
    - - inode object
      - file object
      - superblock object
      - dentry object
- - - - list of file names with pinters to data blocks
      - time consuming to execute
- - - - scattered anywhere in disk
    - - allocating in clusters is preferred :
    - - FAT
      - simple but effiicient
  - - - index block
        
        diffrent schemes
        
        linedk scheme
        
        Multilevel index
        
        combined scheme
- - - - Bit vector
        
        Biut map, each block is represented 1 if free, if not 0
        
        simple
        
        efficient in finding first block
      - Linked list
        
        jelps to keep reference to first free block in memory, this would be inexpensive
      - Grouping
        
        Modification of free'list
        
        Stores address of n free blocks in the first free block
      - counting
        
        Locality principle
        
        rather than keeping list of n free disk, we keep address of the first free block and the nuber of free contigous blocks
      - Space map
        
        Oracle ZFS
        
        designed for huge amounts of files
        
        metaslabs
        
        divides the space into chunks of manegable size
- - - - clustering improves file-seek and transfer
        
        increments fragmentation
  - - - buffer cache
        
        Blocks are kept assuming they will be used soon
      - page cache
        
        virtual memory to cache file data as pages
        
        unified virtual memory
        
        cache both process pages and file data
    - - synchronous
      - asynchrounous
- - - - and correct it
  - - - file systems create logs
        
        Transactions
        
        once in log they are commited
        
        circular buffer stores transactions
      - recovery methods for system crashing
  - - - all data is written to new blocks
        
        old structures point to new ones once it finishes
    - - View of the system before last update took place
  - - - Systems may be backed up and then restored
      - initial backup all files
        
        new changes - incremental backup
- - - - set of independent machines
        
        independent file systems
        
        allow file sharing among systems
  - - - includes
        
        Name of the remote directory
        
        the request is mapped to the RPC and is forwarded to the mount server running on the server machine
        
        the sever machine maintains a
        
        export list
  - - - Searching for a file
      - reading a set of directory entries
      - manopulatiing links and directories
      - accessing file attributes
      - reading and writing files
  - - - Once broken down an NFS lookup is done for every pair