| 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>
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| 9 | Disk image files reside on the host system and are seen by the
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| 10 | guest systems as hard disks of a certain geometry. When a guest OS
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| 11 | reads from or writes to a hard disk, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> redirects the
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| 12 | request to the image file.
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| 13 | </p>
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| 14 | <p>
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| 15 | Like a physical disk, a virtual disk has a size, or capacity,
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| 16 | which must be specified when the image file is created. As opposed
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| 17 | to a physical disk however, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> enables you to expand
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| 18 | an image file after creation, even if it has data already. See
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| 19 | <xref href="vboxmanage-modifymedium.dita"/>.
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| 20 | </p>
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| 21 | <p>
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| 22 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> supports the following types of disk image files:
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| 23 | </p>
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| 24 | <ul>
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| 25 | <li>
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| 26 | <p>
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| 27 | <b outputclass="bold">VDI.</b> Normally, <ph conkeyref="vbox-conkeyref-phrases/product-name"/>
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| 28 | uses its own container format for guest hard disks. This is
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| 29 | called a Virtual Disk Image (VDI) file. This format is used
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| 30 | when you create a new virtual machine with a new disk.
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| 31 | </p>
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| 32 | </li>
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| 33 | <li>
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| 34 | <p>
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| 35 | <b outputclass="bold">VMDK.</b> <ph conkeyref="vbox-conkeyref-phrases/product-name"/> also
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| 36 | fully supports the popular and open VMDK container format that
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| 37 | is used by many other virtualization products, such as VMware.
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| 38 | </p>
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| 39 | </li>
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| 40 | <li>
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| 41 | <p>
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| 42 | <b outputclass="bold">VHD.</b> <ph conkeyref="vbox-conkeyref-phrases/product-name"/> also
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| 43 | fully supports the VHD format used by Microsoft.
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| 44 | </p>
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| 45 | </li>
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| 46 | <li>
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| 47 | <p>
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| 48 | <b outputclass="bold">HDD.</b> Image files of Parallels
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| 49 | version 2 (HDD format) are also supported.
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| 50 | </p>
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| 51 | <p>
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| 52 | Due to lack of documentation of the format, newer versions
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| 53 | such as 3 and 4 are not supported. You can however convert
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| 54 | such image files to version 2 format using tools provided by
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| 55 | Parallels.
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| 56 | </p>
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| 57 | </li>
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| 58 | </ul>
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| 59 | <p>
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| 60 | Irrespective of the disk capacity and format, as mentioned in
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| 61 | <xref href="create-vm-wizard.dita#create-vm-wizard"/>, there are two options for
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| 62 | creating a disk image: fixed-size or dynamically allocated.
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| 63 | </p>
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| 64 | <ul>
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| 65 | <li>
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| 66 | <p>
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| 67 | <b outputclass="bold">Fixed-size.</b> If you create a
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| 68 | fixed-size image, an image file will be created on your host
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| 69 | system which has roughly the same size as the virtual disk's
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| 70 | capacity. So, for a 10 GB disk, you will have a 10 GB file.
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| 71 | Note that the creation of a fixed-size image can take a long
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| 72 | time depending on the size of the image and the write
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| 73 | performance of your hard disk.
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| 74 | </p>
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| 75 | </li>
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| 76 | <li>
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| 77 | <p>
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| 78 | <b outputclass="bold">Dynamically allocated.</b> For
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| 79 | more flexible storage management, use a dynamically allocated
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| 80 | image. This will initially be very small and not occupy any
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| 81 | space for unused virtual disk sectors, but will grow every
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| 82 | time a disk sector is written to for the first time, until the
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| 83 | drive reaches the maximum capacity chosen when the drive was
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| 84 | created. While this format takes less space initially, the
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| 85 | fact that <ph conkeyref="vbox-conkeyref-phrases/product-name"/> needs to expand the image file
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| 86 | consumes additional computing resources, so until the disk
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| 87 | file size has stabilized, write operations may be slower than
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| 88 | with fixed size disks. However, after a time the rate of
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| 89 | growth will slow and the average penalty for write operations
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| 90 | will be negligible.
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| 91 | </p>
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| 92 | </li>
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| 93 | </ul>
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| 94 | </body>
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| 95 |
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| 96 | </topic>
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