File management in UNIX and windows 2000

1
File management in UNIX and windows 2000

• FILE MANAGEMENT
• File Management system is that set of system
  software that provides services to users and
  applications in the use of files.
• The only way that a user or application may
  access files is through the file management
  system.
• This relieves the user or programmer of the
  necessity of developing special-purpose software
  for each application .

2
UNIX File Management

• UNIX file system is hierarchical file system.
• The directory that you are placed when you first
  log on to the system is called the home
  directory.
• System administrator creates the home directory
  for each user.

3
Different Type Of Files

• Ordinary files
• Directories
• Special files
• Pipes

4
Ordinary Files

• This type of file is used to store information,
  such as some text or an image.
• Any file is always contained within a directory.
• Files do not actually reside inside directories.
  A directory is a file that contains references to
  other files. The directory holds two pieces of
  information about each file
•  Its filename.
• An inode number which acts as a pointer to where
  the system can find the information it needs
  about this file.

5
Directories

• A directory is a file that holds other files and
  other directories. You can create directories in
  your home directory to hold files and other
  sub-directories.
• Having your own directory structure gives you a
  definable place to work from and allows you to
  structure your information in a way that makes
  best sense to you.
•  

6
Special Files

• This type of file is used to represent a real
  physical device such as a printer, tape drive or
  terminal.
• It may seem unusual to think of a physical device
  as a file, but it allows you to send the output
  of a command to a device in the same way that you
  send it to a file.

7
Pipes

• UNIX allows you to link commands together using a
  pipe.
• The pipe acts a temporary file which only exists
  to hold data from one command until it is read by
  another.
• The pipe takes the standard output from one
  command and uses it as the standard input to
  another command
•  

8
Structure Of The File System.

• The UNIX file system is organized as a hierarchy
  of directories starting from a single directory
  called root which is represented by a / (slash).
  Imagine it as being similar to the root system of
  a plant or as an inverted tree structure.
• Immediately below the root directory are several
  system directories that contain information
  required by the operating system.
•  

9
Controlling Access To Files And Directories

• Every file and directory in your account can be
  protected from or made accessible to other users
  by changing its access permissions.
• You can only change the permissions for files and
  directories that you own
•  

10
Controlling Access To Files And
Directories(contd.)

• The user has following options
• Displaying access permissions
• Understanding access permissions
• Default access permissions
• Changing group ownership of files and directories
  
• Changing access permissions

11
i-node

• A Unix file is described by an information block
  called an i-node.
• There is an i-node on disc for every file on the
  disc and there is also a copy in kernel memory
  for every open file.
• All the information about a file, other than it's
  name, is stored in the i-node

12
i-node(contd.)

• The following information is contained in the
  i-node
• File access and type information, collectively
  known as the mode.
• File ownership information.
• Time stamps for last modification, last access
  and last mode modification.
• Link count.
• File size in bytes.
• Addresses of physical blocks.

13
Structure of i-node
14
Structure of the i-node(contd.)

• There are 13 physical block addresses in an
  i-node, each of these addresses is 3 bytes long.
• The first ten block addresses refer directly to
  data blocks, the next refers to a first level
  index block
• the next refers to a second level index block
  which holds the addresses of further index blocks
• the last refers to a third level index block
  which holds the addresses of further second level
  index blocks.

15
Windows 2000 File System

•  
• Windows 2000 supports a number of file systems,
  including the file allocation table (FAT) that
  runs on windows 95, MS DOS, and OS/2. But the
  developers of windows 2000 also designed a new
  and a very effective file system, NTFS file
  system

16
NTFS Physical Structure

• The NTFS partition theoretically can be almost of
  any size
• NTFS divides all useful place into clusters -
  data blocks used at a time. NTFS supports almost
  all sizes of clusters - from 512 bytes up to 64
  KBytes. The 4 KBytes cluster is considered to be
  some standard..

17
NTFS Layout
18
Overview Of Partition structure

• NTFS disk is symbolically divided into two parts
• The first 12 of the disk are assigned to
  so-called MFT area (Master File Table). The
  MFT-area is always kept empty not to let the most
  important service file (MFT) be fragmented at
  growth.
• The rest 88 of the disks represent usual space
  for files storage.

19
MFT Its Structure

• The most important file on NTFS is named MFT or
  Master File Table - the common table of files
• MFT is divided into records of the fixed size
  (usually 1 KBytes), and each record corresponds
  to some file.
• The first 16 files are housekeeping and they are
  inaccessible to the operating system. They are
  named metafiles and the very first metafile is
  MTF itself.

20
Features Of NTFS

• Directories
• Journalizing
• Compression
• Security
• Encryption
• Recoverability
•      

21
Directories

• The directory on NTFS is a specific file storing
  the references to other files and directories
  establishing the hierarchical constitution of
  disk data
• The directory file is divided into blocks, each
  of them contains a file name, base attributes and
  reference to the element MFT which already gives
  the complete information on an element of the
  directory.

22
Journalizing

• NTFS is a fail-safe system which can correct
  itself at practically any real failure.
• NTFS just doesn't have intermediate (erratic or
  incorrect) conditions - the data variation
  quantum cannot be divided on before failure or
  after it bringing breakups and muddle - it is
  either accomplished or cancelled.
•  

23
Compression

• Files on the NTFS volume have one rather useful
  attribute - "compressed".
• Any file or directory in the individual order can
  be stored on the disk in the compressed form and
  this process is completely clear for applications
  
• The file compression has very much high speed and
  only one large negative property - huge virtual
  fragmentation of compressed files which however
  does not bother anybody.

24
Security

• NTFS is supposed to be the most perfect file
  system from all nowadays existing.
• In theory it is undoubtedly so, but in current
  implementations unfortunately the rights system
  is far enough from the ideal.
• NTFS file system rights are close connected with
  the system itself, and that means they are not
  obligatory to be kept by another system if it is
  given physical access to the disk

25
Encryption

• Each file or directory can be encrypted and thus
  cannot be read by another NT installation.
• In combination with standard and safe password on
  the system, important data selected by you can be
  protected.

26
Recoverability

• Each file on an NTFS volume is listed as a record
  in a special file called the Master File Table
  (MFT).
• The first record in the table describes the MFT
  itself.
• second record is an MFT "mirror" record. If the
  first MFT record is corrupted, NTFS uses the
  second record to find the MFT mirror file.
• The third record in the MFT is the log file which
  records all file transaction information.

27
Recoverability(contd.)

• If a transaction completes successfully, NTFS
  commits the file update to disk.
• If the transaction is not complete, NTFS ends or
  rolls back the transaction.
• If the system crashes, NTFS performs three passes
  through the data on the disk an analysis pass, a
  redo pass, and an undo pass.

28
Recoverability(contd.)

• The NTFS recovery pass involves the following six
  steps
• When Windows NT recognizes an NTFS volume, it
  reads the MFT.
• NTFS calls the Log File Service to open the log
  file. This causes the Log File Service Recovery
  to take place.
• NTFS calls the Log File Service to read its
  restart area and reads all the data from the last
  checkpoint operation. This data initializes the
  transaction table, dirty pages table, and open
  file table so they can be used in the recovery
  process.
• NTFS performs an analysis pass on its last
  checkpoint record. At the end of this pass, the
  transaction table contains only transactions that
  were active when the
• 5. NTFS performs a redo pass. At the end
  of this pass, the cache reflects the state of the
  volume when the crash occurred.
• 6. NTFS performs an undo pass. At the end
  of this pass, the volume is recovered to a stable
  state

29
Advantages Of NTFS

• The NTFS file system is best for use on volumes
  of about 400 MB or more, because performance does
  not degrade as much on larger NTFS volumes as
  compared to larger FAT volumes
• You can assign permissions to individual files
  and folders, so you can specify who is allowed
  various kinds of access to a file or folder
• You can assign permissions to individual files
  and folders, so you can specify who is allowed
  various kinds of access to a file or folder