File Systems Unix vs. Windows NT

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File SystemsUnix vs. Windows NT

• COSC513 Operation Systems
• Prof. Anvari
• Name Aiwu Li
• SID 103532

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What is a File System?

• The software used to organize and manage the data
  stored on disk drives. In addition to storing the
  data contained in files, a file system also
  stores and manages important information about
  the files and about the file system itself.

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File system Features

• Size of File Systems - as much as a Petabyte.
• EFS was limited to a maximum file system
  size of 8 GB. Many 32-bit file systems are
  limited to 2GB.
• Large Files Many file systems were limited to a
  maximum file size of 2GB. In addition, File I/O
  can be dramatically accelerated by allocating
  disk space contiguously.
• Large Directories Most file systems use linear
  searches, going through a directory entry by
  entry, to locate a particular file. This becomes
  very inefficient when the number of files in a
  directory exceeds a few thousand.

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File system Features ( cont)

• Large numbers of files The only way to
  efficiently scale to support large numbers of
  files is to dynamically allocate index space for
  files.
• Rapid Crash Recovery Many traditional file
  systems require a checking program to check file
  system consistency after a crash. On large,
  active file systems this type of checking can
  take a prohibitively long time to complete.
  Solving this problem must not degrade I/O
  performance.
• Unparalleled Performance Performance should not
  degrade as the size of the file system, an
  individual file or the total number of files
  stored grows.

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Modern File Systems

• UFS The archetypal Unix file system still
  widely available from Unix vendors such as Sun
  and HP.
• VxFS The Veritas File System, a commercially
  developed file system available on a number of
  Unix platforms including Sun and HP.
• NTFS The file system designed by Microsoft for
  Windows NT.

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Measure of memory

• 1 MB ( Megabytes) 220 bytes
• or 106 (1,000,000) bytes,
• 1 GB ( Gigabytes) 230 bytes
• or 109 (1,000,000,000) bytes
• 1 TB ( Terabytes) 240 bytes
• 1 PB ( Petabytes) 250 bytes
• 1 EB ( Exabytes) 260 bytes

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Support for Large File Systems -UFS

• designed at a time when 32-bit computing was the
  norm.
• originally only supported file systems of up to
  231 or 2 GB.
• Most current implementations have been extended
  to support larger file systems.
• i.e. Sun extended UFS in Solaris 2.6 to support
  file systems of up to 1 TB(240 bytes).

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Support for Large File Systems -VxFS

• The maximum file system size supported by VxFS
  depends on the operating system on which it is
  running.
• For instance,
• HP-UX 10---- max FS size is 128 GB.
  HP-UX 11 ----max FS size is 1 TB .

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Support for Large File Systems-NTFS

• NTFS provides a full 64-bit file system,
  theoretically capable of scaling to large sizes.
• However, other limitations result in a
  "practical limit" of 2 TB for a single file
  system.

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Allocation Methods

• Block Allocation- Blocks are allocated one at a
  time and a pointer is kept to each block in the
  file.
• Extent Allocation- Large numbers of contiguous
  blocks - called extents - are allocated to the
  file and tracked as a unit.
• - A pointer need only be maintained to the
  beginning of the extent. Because a single pointer
  is used to track a large number of blocks, the
  bookkeeping for large files is much more
  efficient.

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Support for Large Files -UFS

• Traditional UFS is limited to files no larger
  than 2GB, block allocation is used rather than
  extent allocation, and its algorithms to manage
  very large files and large amounts of free space
  are inefficient.
• 1990 Sun implemented a new algorithm called
  clustering that allows for more extent-like
  behavior by gathering up to 56KB of data in
  memory to allocate disk space contiguously.
• Sun also extended the maximum file size to 1TB in
  Solaris 2.6.

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Support for Large Files -VxFS

• The maximum file size supported by VxFS depends
  on the version.
• For HP-UX 11 it is 1 TB. VxFS uses extent based
  allocation. The maximum extent size is 64MB for
  VxFS.

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Support for Large Files -NTFS

• Support up file size to 2 TB.
• The disk space allocation mechanism in NTFS is
  essentially extent-based.
• Each file in NTFS is mapped by an entry in the
  master file table or MFT.
• The NTFS literature refers to logical blocks as
  clusters. Allowable cluster sizes range from 512
  bytes to 64 KB, depend on volume size.

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Rapid Crash Recovery - UFS

• Traditional UFS did not provide journaling.
• In case of a system failure, the program fsck is
  used by UFS to check the file system.
• The key point is that everything must be checked
  whether it has been changed recently or not.
• Sun implemented an optional journal for the UFS
  file recovery in Solaris 2.7.

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Rapid Crash Recovery - VxFS

• VxFS employs a metadata journaling scheme for
  recovery.
• The VxFS log is synchronous. In addition to
  metadata logging, VxFS allows small synchronous
  writes to be logged as well. This could be
  advantageous for databases running within the
  file system.
• VxFS does allow the log to be placed on a
  separate device if desired.

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Rapid Crash Recovery - NTFS

• NTFS also uses a synchronous metadata journal to
  a log file that is typically a few megabytes in
  size.
• As such, the log cannot be allocated on a
  separate device to enhance performance.
• The FAT file system doesnt offer any of these
  features. FAT does maintain two copies of the
  file-allocation table, in case one copy is
  damaged, instead, you must run a utility such as
  Scandisk.

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Other unique features

• UFS-Because of its long lifespan, UFS has been
  enhanced in many areas. However, none of its
  incarnations has any single unique feature that
  all the others lack. In many senses UFS still
  serves as a precursor of VxFS and other advanced
  Unix file systems.
• VxFS-Veritas promotes the on-line administration
  features of VxFS and its support for databases.
  On-line features include ability to grow or
  shrink a file system, snapshot backup and
  defragmentation.
• NTFS- Compare with FAT, the sole unique feature
  of NTFS is its support for compression, which
  allows files to be compressed individually, by
  folder or by volume.(NTFS 5.0 supports
  encryption).

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Feature comparison among UFS, VxFS, FAT, NTFS
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Conclusion

• UFS has been in use for years, so many system
  administrators are familiar and comfortable with
  it.
• VxFS provides modest improvements over UFS and
  works well in many environments.
• NTFS is the only advanced file system currently
  available for Windows NT, and therefore has a
  captive audience.

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Reference

• Avi Silberschatz, Peter Galvin. Applied Operating
  System Concept. New York John Wiley, 2000.
• Overview of FAT, HPFS, and NTFS File System.
  Microsoft Product Support Service. March, 2000
• Jeffrey Richter and Luis Felipe Cabera. A File
  System for the 21th century Previewing the
  Window NT 5.0 File System. Microsoft System
  Journal. November 1998.
• Choosing between FAT and NTFS. Microsoft Product
  Support Service. March 2000
• Avi Silberschatz. Operating System Concepts.
• Philip Trautman and Jim Mostek. Scalability and
  Performance in Modern File Systems.
• Custer, Helen. Inside the Windows NT File System.
  Microsoft Press(1998). Microsoft Corporation