Logical disk

A logical disk, logical volume or virtual disk (VD or vdisk for short) is a virtual device that provides an area of usable storage capacity on one or more physical disk drive(s) in a computer system. The disk is described as logical or virtual because it does not actually exist as a single physical entity in its own right. The goal of the logical disk is to provide computer software with what seems a contiguous storage area, sparing them the burden of dealing with the intricacies of storing files on multiple physical units. Most modern operating systems provide some form of logical volume management.

Logical disks can be defined at various levels in the storage infrastructure.

An operating system may define volumes or logical disks and assign each to one physical disk, more than one physical disk or part of the storage area of a physical disk. For example, Windows NT can create several partitions on a hard disk drive, each of which a separate volume with its own file system. Each floppy disk drive, optical disc drive or USB flash drive in Windows NT becomes one volume. Windows NT can also create partitions that span multiple hard disks drives. Each volume is identified with a drive letter.

Storage area networks (SANs) consolidate inhomogeneous storage devices. As such logical disks or vdisks allow computer programs to access files stored on a SAN.

A hardware-level redundant array of independent disks (RAID) exposes itself to the operating system as one logical disk while the array itself consists of several disks. The operating system either does not know that the hardware with which it is interfacing is a RAID, or knows but still does not concern itself with intricate details of storage. In case of the latter, specialized management, maintenance and diagnostics software dedicated to that specific RAID may run on the operating system.

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