| 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>
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| 8 | As an alternative to using virtual disk images as described in
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| 9 | <xref href="storage.dita">Virtual Storage</xref>, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> can also present
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| 10 | either entire physical hard disks or selected partitions as
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| 11 | virtual disks to virtual machines.
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| 12 | </p>
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| 13 | <p>
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| 14 | With <ph conkeyref="vbox-conkeyref-phrases/product-name"/>, this type of access is called <i>raw
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| 15 | hard disk access</i>. It enables a guest operating system
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| 16 | to access its virtual hard disk without going through the host
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| 17 | OS file system. The actual performance difference for image
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| 18 | files compared to raw disk varies greatly depending on the
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| 19 | overhead of the host file system, whether dynamically growing
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| 20 | images are used, and on host OS caching strategies. The caching
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| 21 | indirectly also affects other aspects such as failure behavior.
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| 22 | For example, whether the virtual disk contains all data written
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| 23 | before a host OS crash. Consult your host OS documentation for
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| 24 | details on this.
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| 25 | </p>
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| 26 | <note type="attention">
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| 27 | <p>
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| 28 | Raw hard disk access is for expert users only. Incorrect use
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| 29 | or use of an outdated configuration can lead to
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| 30 | <b outputclass="bold">total loss of data</b> on the
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| 31 | physical disk. Most importantly, <i>do not</i>
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| 32 | attempt to boot the partition with the currently running host
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| 33 | operating system in a guest. This will lead to severe data
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| 34 | corruption.
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| 35 | </p>
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| 36 | </note>
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| 37 | <p>
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| 38 | Raw hard disk access, both for entire disks and individual
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| 39 | partitions, is implemented as part of the VMDK image format
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| 40 | support. As a result, you will need to create a special VMDK
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| 41 | image file which defines where the data will be stored. After
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| 42 | creating such a special VMDK image, you can use it like a
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| 43 | regular virtual disk image. For example, you can use the Virtual
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| 44 | Media Manager, see <xref href="virtual-media-manager.dita">The Virtual Media Manager</xref>, or
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| 45 | <userinput>VBoxManage</userinput> to assign the image to a virtual
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| 46 | machine.
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| 47 | </p>
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| 48 | </body>
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| 49 | </topic>
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