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<title>Logical disk</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Logical disk</span></span>

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</style><div role="note" class="hatnote navigation-not-searchable">"VDisk" and "vdisk" redirect here. For the RAM disk driver, see <a href="VDISK.SYS" class="mw-redirect" title="VDISK.SYS">VDISK.SYS</a>. For the World War II phonographic records, see <a href="V-Disc" title="V-Disc">V-Disc</a>.</div>

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<p>A <b>logical disk</b>, <b>logical volume</b> or <b>virtual disk</b> (<b>VD</b><sup id="cite_ref-:0_1-0" class="reference"><a href="#cite_note-:0-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> or <b>vdisk</b><sup id="cite_ref-:1_2-0" class="reference"><a href="#cite_note-:1-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> for short) is a <a href="Virtual_device" title="Virtual device">virtual device</a> that provides an area of usable storage capacity on one or more physical <a href="Disk_drive" class="mw-redirect" title="Disk drive">disk drive</a>(s) in a computer system. The disk is described as <i>logical</i> or <i>virtual</i> 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 <a href="Operating_systems" class="mw-redirect" title="Operating systems">operating systems</a> provide some form of <a href="Logical_volume_management" title="Logical volume management">logical volume management</a>.

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<div class="mw-heading mw-heading2"><h2 id="Levels">Levels</h2></div>

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

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<div class="mw-heading mw-heading3"><h3 id="Operating_system">Operating system</h3></div>

<p>An operating system may define <a href="Volume_(computing)" title="Volume (computing)"><i>volumes</i> or <i>logical disks</i></a> and assign each to one physical disk, more than one physical disk or part of the storage area of a physical disk. For example, <a href="Windows_NT" title="Windows NT">Windows NT</a> can <a href="Disk_partitioning" title="Disk partitioning">create several partitions</a> on a <a href="Hard_disk_drive" title="Hard disk drive">hard disk drive</a>, each of which a separate volume with its own <a href="File_system" title="File system">file system</a>. Each <a href="Floppy_disk" title="Floppy disk">floppy disk drive</a>, <a href="Optical_disc_drive" title="Optical disc drive">optical disc drive</a> or <a href="USB_flash_drive" title="USB flash drive">USB flash drive</a> in Windows NT becomes one volume. Windows NT can also create <a href="Dynamic_disk" class="mw-redirect" title="Dynamic disk">partitions that span multiple hard disks drives</a>. Each volume is identified with a <a href="Drive_letter_assignment" title="Drive letter assignment">drive letter</a>.

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<div class="mw-heading mw-heading3"><h3 id="Storage_area_network">Storage area network</h3></div>

<p><a href="Storage_area_network" title="Storage area network">Storage area networks</a> (SANs) consolidate inhomogeneous storage devices. As such <i>logical disk</i>s or <i>vdisk</i>s allow computer programs to access files stored on a SAN.<sup id="cite_ref-:0_1-1" class="reference"><a href="#cite_note-:0-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-:1_2-1" class="reference"><a href="#cite_note-:1-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading3"><h3 id="Storage_subsystem">Storage subsystem</h3></div>

<p>A hardware-level <a href="RAID" title="RAID">redundant array of independent disks</a> (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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<div class="mw-heading mw-heading2"><h2 id="Motivation">Motivation</h2></div>

<p>When <a href="IBM" title="IBM">IBM</a> first released the <a href="Magnetic_disk" class="mw-redirect" title="Magnetic disk">magnetic disk</a> drive in the 1956 <a href="IBM_305" class="mw-redirect" title="IBM 305">IBM 305</a>, a single disk drive would be directly attached to each system, managed as a single entity. As the development of drives continued, it became apparent that reliability was a problem and systems using RAID technology evolved, so that more than one physical disk is used to produce a single logical disk.

</p><p>Many modern business <a href="Information_technology" title="Information technology">information technology</a> environments use a SAN. Here, many storage devices are connected to many host <a href="Server_(computing)" title="Server (computing)">server</a> devices in a network. A single RAID array may provide some capacity to one server, and some capacity to another. Therefore, logical disks are used to partition the available capacity and provide the amount of storage needed by each host from a common pool of logical disks. The <a href="IBM_SAN_Volume_Controller" title="IBM SAN Volume Controller">IBM SAN Volume Controller</a> uses the term "vdisk" to refer to these logical disks.<sup id="cite_ref-:1_2-2" class="reference"><a href="#cite_note-:1-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

</p><p>Today, the rationale for the logical disk approach starts to be questioned<sup id="cite_ref-Storagebod_3-0" class="reference"><a href="#cite_note-Storagebod-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> and solutions that offer more flexibility and better abstraction are increasingly needed.

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<ul><li><a href="Storage_virtualization" title="Storage virtualization">Storage virtualization</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite id="CITEREFBuyyaBrobergGoscinski2010" class="citation book cs1">Buyya, Rajkumar; Broberg, James; Goscinski, Andrzej M. (2010). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=S1NvRRd77rQC&q=VD"><i>Cloud Computing: Principles and Paradigms</i></a>. John Wiley & Sons. p. 664. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>9781118002209</bdi>.</cite></span>

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<li id="cite_note-:1-2"><span class="mw-cite-backlink">^ <a href="#cite_ref-:1_2-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:1_2-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-:1_2-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text"><cite id="CITEREFSmith2011" class="citation book cs1">Smith, Hubbert (2011). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=zIr_5Ls9LxcC&pg=PT309"><i>Data Center Storage: Cost-Effective Strategies, Implementation, and Management</i></a>. CRC Press. p. 309. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>9781466507814</bdi>.</cite></span>

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<li id="cite_note-Storagebod-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-Storagebod_3-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFThe_Register2013" class="citation news cs1">The Register (2013). <a rel="nofollow" class="external text" href="https://www.theregister.co.uk/2013/10/08/luns_are_the_bane_of_every_storage_sysadmins_life_kill_them_now/">"The LUN must DIE. Are you with me, storage bods?"</a>.</cite></span>

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</style><div id="Storage_virtualization26" style="font-size:114%;margin:0 4em"><a href="Storage_virtualization" title="Storage virtualization">Storage virtualization</a></div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Block-level_storage" title="Block-level storage">Block-level storage</a></li>

<li><a href="Disk_aggregation" title="Disk aggregation">Disk aggregation</a></li>

<li><a href="Distributed_file_system" class="mw-redirect" title="Distributed file system">Distributed file systems</a>

<ul><li><a href="Comparison_of_distributed_file_systems" title="Comparison of distributed file systems">Comparison</a></li></ul></li>

<li><a href="File_virtualization" title="File virtualization">File virtualization</a></li>

<li><a href="Software-defined_storage" title="Software-defined storage">Software-defined storage</a></li>

<li><a href="Virtual_disk_and_virtual_drive" title="Virtual disk and virtual drive">Virtual disk</a></li>

<li><a href="Virtual_file_system" title="Virtual file system">Virtual file system</a></li></ul>

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