Disk Partitioning

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Disk Partitioning

• By Stefano Polo

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Overview

• Creating divisions on a Hard Disk
• Directories and files are then grouped by
  categories
• Data types
• Usage
• Partitions contains file systems
• Space Management
• Access Permissions
• Directory Searching

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Overview cont.

• A file system can decide how many separate
  categories of data are needed and the size of
  each.
• Seperating operating system from user files

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Examples

• Partition for Swapping
• Keeps frequently used programs and data near each
  other
• Keeping browser cache files in separate
  partitions keeps them away from each other
• Seperating email from audio and photos

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Benefits

• The Use of Multi-booting setups
• Having more than 1 operating system
• Sharing swap partitions between multiple linux
  distributions
• Allows the need for less memory
• Protecting and isolating files
• Easy to recover corrupted file systems and
  operating systems installed
• Increase Computer performance
• Smaller file systems are more efficient
• Higher level of data organization
• Keeping videos, photos, audios, emails,
  etcseperated

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PC Bios Partition Types

• Used in MS-Dos, Windows, Linux
• Can contain up to 4 Primary or 1-3 primary and 1
  extended
• Each partition have 16-byte entries in the
  partition table located in the Master Boot Record
• A primary partition contains one file system

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Primary (Logical)

• The "partition type" code for a primary or
  logical partition can either correspond to a file
  system contained within (e.g. 0x07 means either
  an NTFS or an OS/2 HPFS file system) or indicate
  the partition has a special use (e.g. code 0xBC
  may mean an Acronis Secure Zone and code 0x82
  usually indicates a Linux swap partition). The
  FAT16 and FAT32 file systems have made use of
  quite a number of partition type codes over time
  due to the limits of various DOS and Windows OS
  versions. Though a Linux operating system may
  recognize a number of different file systems
  (ext2, ext3, reiserfs, etc.), they have all
  consistently used the same partition type code
  0x83 (Linux native). (wikipedia)

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NTFS

• All file data are stored as metadata
• Simply just data about data
• May describe individual datum, content item, or a
  collection of data
• Allows any sequence of 16-bit values for name
  encoding
• uses B trees to index file system data
• Master File Table (MFT) contains metadata about
  every file, directory, and metafile on an NTFS
  volume

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File Allocation Table (FAT)

• Used mostly today in floppies and solid-state
  memory cards (flash memory)
• Gives convenience towards sharing data between
  operating systems on one machine
• Uses a table which contains information on which
  areas that belong to files are free or unusable
• Table also gives information on where the data is
  actually stored
• To limit the size of the table, disk space is
  allocated in hardware sectors called clusters
• Maximum numbers of clusters have increased over
  time
• the number of bits required to identify a cluster
  is used to name the successive major versions of
  the format
• Fat12
• Fat16
• Fat32

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Drawbacks of FAT

• When files are deleted and new files are created,
  directory fragments tend to get scattered over
  the entire disk
• This causes slow read/write processes
• Defragmentation can solve this issue
• Can be a lengthy process
• Would need to be performed reguraly
• Solid-State should not be defragmented since they
  tend to wear down eventually

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Extended

• Secondary to primary partitions
• Hard disk may contain 1 extended partition
• Can be sub-divided into logical drives
• Each are assigned additonal letter drives
• Examples
• Primary partition would be C
• Extended partition would be E, G etc

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Compressed Disks

• Compressed to create additional space
• Creating one large file in a partition
• Storing the disks data in this file
• At startup, device drivers open this file and
  assign it to a separate letter
• To avoid confusion, the original partition and
  the compressed drive had their letters swapped
• Compressed disk would be C
• Uncompressed disk were given higher names

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Partitioning Schemes

• Microsoft
• create a single active primary partition, the C
  drive
• Where all system, user data, applications, and
  page file all reside
• Some users, however, prefer to create multiple
  partitions so that the operating system can be
  stored separately from other kinds of data.

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Partitioning Schemes cont.

• Unix
• creation of separate partitions for /boot, /home,
  /tmp, /usr, /var, /opt, swap and all remaining
  files under the "/" (root directory)
• Advantages
• if one file system gets corrupted, the rest of
  the data (the other file systems) stay intact,
  minimizing data loss
• can be accessed read-only and the execution of
  setuid files disabled thus enhancing security
• performance may be enhanced due to less disk head
  travel

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Partitioning Schemes cont.

• Disadvantages of Unix scheme partition
• user could run out of hard drive space in his or
  her /home partition
• good implementation requires the user to predict
  how much space each partition will need, which
  may be a difficult task
• Logical Volume Management, often used in servers,
  increases flexibility by allowing data in volumes
  to expand into separate physical disks
• Another option is to resize existing partitions
  when necessary.

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Partition Recovery

• When a partition is deleted, generally only the
  table entry is removed
• The data is still on the hard disk but maybe
  un-accessible
• Specialized recovery tools can access the data
  and recreate the table entry
• Some disk utilities may also overwrite a number
  of beginning sectors of a partition they delete
• In this case it may be possible to restore a
  FAT32 or NTFS partition if a backup boot sector
  is available