M3_Review-Chapter11

# CSC360
Operating Systems

Midterm #3 review.

Mass Storage Structure - Chapter 10

Slides: File Systems

  File Concepts
    □ File: Logical storage unit for information
    □ File type: data (text, binary, ...), program
    □ File Attributes: Meta information
      □ name, size, time, owner, protection, location, ...
      □ kept in directory, (a special file)
    □ File Operations:
      □ create, write, seek, append, truncate, etc
      
  File Structures:
    □ is how information is organized within a file
      □ unstructured
      □ structured with records. 
      □ Examples:
        □ binary executable
        □ binary archive
          □ modules
  
  File Access:
    □ Sequential access
      □ variable length records.
      □ to access record ri, go through r1 to ri-1 first
    
    □ Direct Access
      □ fixed length records of size s
      □ i-th record: offset n(i-1)*s
    
    □ indexed access
      □ access index first
      
  Directory Concepts:
    □ A special file
      □ a collection of meta information of files.
      □ normally structured
      □ and allow direct access
    
    □ directory operations
      □ "file: operations on directory records
    
    □ File system on disk
      □ partitions, file Systems (FAT, FDT), files
      
  Acyclic-graph Directories:
    Links: effectively another pointer to a file or subdirectory
      □ HardLink:
        □ isnt a pointer to a file. its a directory entry (a file) pointing to the same inode. Even if you change the name
          of the other file, a hardlink still points to the file. (reference to an object)
      □ Symbolic link:
        □ points to another path (a filename).
        □ resolves the name of the file each time you access it through the symlink.
        □ if the file is removred, the symlink will not follow.
          □ if the file is replaced with a file of the same name the symbolic link will point to the new file. 
        □ can span filesystems.
        □ only contains information about the path to the file does not care about the file at all. no information about the 
          file.
    
    resolve:
      □ we resolve the link by using that path name to locate the real file.
      
  File System Operationgs:
    □ Mount File Systems:

  File sharing and protection:
    □ File Attributes:
      □ owner: userID, group ID
    □ type of access:
      □ read, write, execute, etc.
    □ Share over the network. 
      □ Host id
      □ NFS: network file systems.
        □ remote procedure calls
      
  Failure Mode:
    □ Local file systems:
      □ hardware failure
      □ corrupted information
    □ remote file systems:
      □ network failure
    □ Fault-tolerant systems:
      □ keep state at both sides, or
      □ stateless but less secure
      
  Consistency control
    □ multiple users access a file simultaneously
      □ lock!
        □ entire file or
        □ certain records
      □ complexity and (network) overhead
    □ consistency semantics:
      □ unix semantics: write immediately visible
      □ session (open()-close()) semantics: eg. AFS