| 1 | <?xml version="1.0" encoding="UTF-8"?>
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| 2 | <!DOCTYPE topic
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| 3 | PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
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| 4 | <topic xml:lang="en-us" id="vdidetails">
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| 5 | <title>Disk Image Files (VDI, VMDK, VHD, HDD)</title>
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| 6 |
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| 7 | <body>
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| 8 | <p>Disk image files reside on the host system and are seen by the guest systems as hard disks of a
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| 9 | certain geometry. When a guest OS reads from or writes to a hard disk, <ph
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| 10 | conkeyref="vbox-conkeyref-phrases/product-name"/> redirects the request to the image file. </p>
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| 11 | <p>Like a physical disk, a virtual disk has a size, or capacity, which must be specified when the image
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| 12 | file is created. As opposed to a physical disk however, <ph conkeyref="vbox-conkeyref-phrases/product-name"/>
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| 13 | enables you to expand an image file after creation, even if it has data already. See <xref
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| 14 | href="vboxmanage-modifymedium.dita"/>. </p>
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| 15 | <p>
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| 16 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> supports the following types of disk image files:
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| 17 | </p>
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| 18 | <ul>
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| 19 | <li>
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| 20 | <p><b outputclass="bold">VDI.</b> Normally, <ph conkeyref="vbox-conkeyref-phrases/product-name"/>
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| 21 | uses its own container format for guest hard disks. This is called a Virtual Disk Image (VDI) file. This
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| 22 | format is used when you create a new virtual machine with a new disk. </p>
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| 23 | </li>
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| 24 | <li>
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| 25 | <p><b outputclass="bold">VMDK.</b>
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| 26 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> also fully supports the popular and open VMDK container
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| 27 | format that is used by many other virtualization products, such as VMware. </p>
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| 28 | </li>
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| 29 | <li>
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| 30 | <p><b outputclass="bold">VHD.</b>
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| 31 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> also fully supports the VHD format used by Microsoft. </p>
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| 32 | </li>
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| 33 | <li>
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| 34 | <p><b outputclass="bold">HDD.</b> Image files of Parallels version 2 (HDD format) are also
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| 35 | supported. </p>
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| 36 | <p>Due to lack of documentation of the format, newer versions such as 3 and 4 are not supported.
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| 37 | You can however convert such image files to version 2 format using tools provided by Parallels. </p>
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| 38 | </li>
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| 39 | </ul>
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| 40 | <p>Irrespective of the disk capacity and format, as mentioned in <xref
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| 41 | href="create-vm-wizard.dita#create-vm-wizard"/>, there are two options for creating a disk image: fixed-size or
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| 42 | dynamically allocated. </p>
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| 43 | <ul>
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| 44 | <li>
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| 45 | <p><b outputclass="bold">Fixed-size.</b> If you create a fixed-size image, an image file will be
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| 46 | created on your host system which has roughly the same size as the virtual disk's capacity. So, for a 10 GB
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| 47 | disk, you will have a 10 GB file. Note that the creation of a fixed-size image can take a long time depending
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| 48 | on the size of the image and the write performance of your hard disk. </p>
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| 49 | </li>
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| 50 | <li>
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| 51 | <p><b outputclass="bold">Dynamically allocated.</b> For more flexible storage management, use a
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| 52 | dynamically allocated image. This will initially be very small and not occupy any space for unused virtual
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| 53 | disk sectors, but will grow every time a disk sector is written to for the first time, until the drive reaches
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| 54 | the maximum capacity chosen when the drive was created. While this format takes less space initially, the fact
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| 55 | that <ph conkeyref="vbox-conkeyref-phrases/product-name"/> needs to expand the image file consumes additional
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| 56 | computing resources, so until the disk file size has stabilized, write operations may be slower than with
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| 57 | fixed size disks. However, after a time the rate of growth will slow and the average penalty for write
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| 58 | operations will be negligible. </p>
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| 59 | </li>
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| 60 | </ul>
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| 61 | </body>
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| 62 |
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| 63 | </topic>
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