| 1 | <?xml version='1.0' encoding='UTF-8'?>
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| 2 | <!DOCTYPE topic PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
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| 3 | <topic xml:lang="en-us" id="rawdisk">
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| 4 | <title>Using a Raw Host Hard Disk From a Guest</title>
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| 5 |
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| 6 | <body>
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| 7 | <p>As an alternative to using virtual disk images as described in <xref href="storage.dita">Virtual Storage</xref>,
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| 8 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> can also present either entire physical hard disks or
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| 9 | selected partitions as virtual disks to virtual machines. </p>
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| 10 | <p>With <ph conkeyref="vbox-conkeyref-phrases/product-name"/>, this type of access is called <i>raw hard disk
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| 11 | access</i>. It enables a guest operating system to access its virtual hard disk without going through the host
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| 12 | OS file system. The actual performance difference for image files compared to raw disk varies greatly depending on
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| 13 | the overhead of the host file system, whether dynamically growing images are used, and on host OS caching
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| 14 | strategies. The caching indirectly also affects other aspects such as failure behavior. For example, whether the
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| 15 | virtual disk contains all data written before a host OS crash. Consult your host OS documentation for details on
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| 16 | this. </p>
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| 17 | <note type="caution">
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| 18 | <p>Raw hard disk access is for expert users only. Incorrect use or use of an outdated configuration can lead to <b
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| 19 | outputclass="bold">total loss of data</b> on the physical disk. Most importantly, <i>do not</i> attempt to
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| 20 | boot the partition with the currently running host operating system in a guest. This will lead to severe data
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| 21 | corruption. </p>
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| 22 | </note>
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| 23 | <p>Raw hard disk access, both for entire disks and individual partitions, is implemented as part of the VMDK image
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| 24 | format support. As a result, you will need to create a special VMDK image file which defines where the data will
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| 25 | be stored. After creating such a special VMDK image, you can use it like a regular virtual disk image. For
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| 26 | example, you can use the Virtual Media Manager, see <xref href="virtual-media-manager.dita">The Virtual Media
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| 27 | Manager</xref>, or <userinput>VBoxManage</userinput> to assign the image to a virtual machine. </p>
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| 28 | </body>
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| 29 | </topic>
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