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Encyclopedia > Volume (computing)

Introduction and Definition

In the context of computer operating systems, "volume" is the term used to describe a single accessible storage area with a single filesystem, typically (though not necessarily) resident on a single partition of a hard disk. Similarly, it refers to the logical interface used by an operating system to access data stored on some media using a single instance of a filesystem. "Volume" can be used in place of the term "drive" where it is desirable to indicate that the entity in question is not a physical disk drive, but rather the corporate data stored using a filesystem there. "Logical drive" and "volume" should be considered synonymous, however "volume" and "partition" are not synonymous. In Unix-like operating systems, volumes usually handled by LVM and manipulated using mount(8). The term is also used with respect to Microsoft Windows NT operating systems (including Windows 2000 and XP), where they are handled by the kernel and managed using the Disk Manager MMC snap-in. In computing, an operating system ( aka, OS) is the system software responsible for the direct control and management of hardware and basic system operations. ... See Filing system for this term as it is used in libraries and offices In computing, a file system is a method for storing and organizing computer files and the data they contain to make it easy to find and access them. ... In general, a partition is a splitting into parts. ... Typical hard drives of the mid-1990s. ... The term drive has several common meanings: Drive is an international alternative rock band based in Monaco known for their rock melodies and introspective lyrics. ... A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. ... LVM is an implementation of a logical volume manager for the Linux kernel. ... Microsoft Corporation (NASDAQ: MSFT, HKEx: 4338) is the worlds largest software company, with 2005 global annual sales of 40 billion US dollars and nearly 60,000 employees in 85 countries and regions. ... Windows NT is a family of operating systems produced by Microsoft, and was succeeded by Windows 2000 (still based on Windows NT). ...

Contents


Differences between Volume and Partition

A volume is not the same thing as a partition. For example, a floppy disk might be accessible as a volume, even though it does not contain a partition, as floppy disks cannot be partitioned with most modern computer hardware. Also, an OS can recognize a partition without recognizing any volume associated with it, as when the OS cannot interpret the filesystem stored there. This situation occurs, for example, with Windows NT-based OSes and most non-Microsoft OS partitions, such as with the EXT3 filesystem commonly used with Linux. A floppy disk is a data storage device that is composed of a ring of thin, flexible (i. ... The ext3 or third extended filesystem is a journalled file system that is coming into increasing use among users of the Linux operating system. ... Tux, a cartoon penguin frequently featured sitting, is the official Linux mascot. ...


Example

This example concerns a Windows XP system with two physical hard disks. The first hard disk has two partitions, the second has only one. The first partition of the first hard disk contains the operating system. Mount points have been left at defaults.

Physical Disk Parition Filesystem Drive Letter
Hard Disk 1 Partition 1 NTFS C:
Partition 2 FAT-32 D:
Hard Disk 2 Partition 1 FAT-32 E:

In this example,

  • "C:", "D:", and "E:" are volumes
  • Hard Disk 1 and Hard Disk 2 are physical disks
  • Any of these can be called a "drive"

Nomenclature of volumes

Windows-NT based operating systems

It is important to note that Windows NT-based OSes do not have a single root directory. As a result, Windows will assign at least one path to each mounted volume, which will take one of two forms:

  • A drive letter, in the form of a single letter followed by a colon, such as "F:"
  • A mount-point on an NTFS volume having a drive letter, such as "C:Music"

In these two examples, a file called "Track 1.mp3" stored in the root directory of the mounted volume could be referred to as "F:Track 1.mp3" or "C:MusicTrack 1.mp3" respectively.


In order to assign a mount point for a volume as a path within another volume, the following criteria must be met:

  • The volume must be formatted NTFS
  • A folder must exist at the root path
  • That folder must be empty

By default, Windows will assign drive letters to all drives, as follows:

  • "A:" and "B:" to floppy disk drives, present or not
  • "C:" and subsequent letters, as needed, to:
    • Hard Disks
    • Removable Disks, including optical media (e.g. CDs and DVDs)

Because of this convention, the operating system startup drive is most commonly called "C:". This is not always the case.


On Windows XP, mount points may be managed through the Disk Management snap-in for the Microsoft Management Console. This can be most conveniently accessed through "Computer Management" in the "Administrative Tools" section of the Control Panel. Windows XP is a major revision of the Microsoft Windows operating system created for use on desktop and business computer systems. ... Categories: Technology stubs | Technology ...


More than one drive letter can reffer to a single volume, as when using the SUBST command.


Warning: removing drive letters or mount-points for a drive may break some programs, as some files may not be accessible under the known path. For example, if a program is installed at "D:Program FilesSome Program", it may expect to find it's data files at "D:Program FilesSome ProgramData". If the logical disk previously called "D:" has it's drive letter changed to "E:", "Some Program" won't be able to find it's data at "D:Program FilesSome ProgramData", since the drive letter "D:" no longer represents that volume.


Unix-like Operating Systems

In Unix-like operating systems, volumes other than the boot volume have a mount-point somewhere with the filesystem, represented by a path. Logically, the directory tree stored on the volume is grafted in at the mountpoint. By convention, mount-points will often be placed in a directory called '/mnt', though '/media' and other terms are sometimes used. A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. ...


Like in Windows, to use a given path as a mount-point for another volume, an empty directory (sometimes called a folder) must exist there.


Unix-like operating systems use the mount command to manipulate mount points for volumes. Mount can mean: a horse or other animal or bird intended for riding; for example, a horse, camel, elephant, or Garuda an attachment point for equipment to vehicles, usually made to enable the object mounted there to be moved in relation to the vehicle, but still remain affixed. ...


For example, if a CD-ROM drive containg a text file called 'info.txt' was mounted at '/mnt/iso9660', the text file would be accessible at '/mnt/iso9660/info.txt'.


Benefits of keeping files within a single volume

Speed of data management

Files within a volume can generally be moved to any other place within that volume by manipulating the filesystem, without moving the actual data. However, if a file is to be moved outside the volume, the data itself must be relocated, which is a much more intensive operation.


In order to better visualize this concept, one might consider the example of a large library. If a non-fiction work is origionally classified as having the subject "plants", but then has to be moved to the subject "flora", one does not need to refile the book, who's position on the shelf would be static, but rather, one needs only to replace the index card. However, to move the book to another library, adjusting index cards alone is insufficient. The entire book must be moved. An index card is a piece of heavy paper stock, cut to a standard size and often used for recording individual items of information that can then be easily rearranged and filed. ...


Special functions of advanced filesystems and volumes

Some filesystems, such as Microsoft's proprietary NTFS filesystem and EXT3, allow multiple pseudonyms ("hard links") to be created for a single file within the same volume. (Hard links cannot be created for files between volumes, this is comparable to moving the file in the library example above.) Hard links allow a file to be referenced by two separate filenames, without it's data being stored in two places on the disk (and thereby consuming twice as much space). To return to the library analogy, this is like filing two index cards for the same book: one could file the above book under both 'flora' and 'plants'. In general, deleting one hard link does not immediately effect other hard links, while deleting the final hard link for a file frees the disk space occupied by that file. However, modifying the data of the file referred to by one hard link will impact all other hard links as well. In the library, this is comparable to writting in the book. Hard links should not be confused with aliases (MacOS), shortcuts (Windows), or soft links (UNIX & variants), which can refer to files on another volume in some cases. FAT filesystems, such as FAT-32, do not support hard or soft links as such, although the Windows operating system supports 'links', which are somewhat less capable. NTFS or New Technology File System is the standard file system of Windows NT and its descendants Windows 2000, Windows XP and Windows Server 2003. ... The ext3 or third extended filesystem is a journalled file system that is coming into increasing use among users of the Linux operating system. ... In computing, a hard link is a reference, or pointer, to the physical data on a volume. ... Everything2, or E2 for short, is a large collaborative Internet community, currently at www. ...


See also

  • MSDN's article on Hard Links and Junctions

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