| 1 | <?xml version="1.0" encoding="UTF-8"?>
|
|---|
| 2 | <!DOCTYPE topic
|
|---|
| 3 | PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
|
|---|
| 4 | <topic xml:lang="en-us" id="snapshots-contents">
|
|---|
| 5 | <title>Snapshot Contents</title>
|
|---|
| 6 |
|
|---|
| 7 | <body>
|
|---|
| 8 | <p>Think of a snapshot as a point in time that you have preserved. More formally, a snapshot consists
|
|---|
| 9 | of the following: </p>
|
|---|
| 10 | <ul>
|
|---|
| 11 | <li>
|
|---|
| 12 | <p>The snapshot contains a complete copy of the VM settings, including the hardware
|
|---|
| 13 | configuration, so that when you restore a snapshot, the VM settings are restored as well. For example, if you
|
|---|
| 14 | changed the hard disk configuration or the VM's system settings, that change is undone when you restore the
|
|---|
| 15 | snapshot. </p>
|
|---|
| 16 | <p>The copy of the settings is stored in the machine configuration, an XML text file, and thus
|
|---|
| 17 | occupies very little space. </p>
|
|---|
| 18 | </li>
|
|---|
| 19 | <li>
|
|---|
| 20 | <p>The complete state of all the virtual disks attached to the machine is preserved. Going back
|
|---|
| 21 | to a snapshot means that all changes that had been made to the machine's disks, file by file and bit by bit,
|
|---|
| 22 | will be undone. Files that were since created will disappear, files that were deleted will be restored,
|
|---|
| 23 | changes to files will be reverted. </p>
|
|---|
| 24 | <p>Strictly speaking, this is only true for virtual hard disks in "normal" mode. You can
|
|---|
| 25 | configure disks to behave differently with snapshots, see <xref href="hdimagewrites.dita#hdimagewrites"/>. In
|
|---|
| 26 | technical terms, it is not the virtual disk itself that is restored when a snapshot is restored. Instead, when
|
|---|
| 27 | a snapshot is taken, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> creates differencing images which
|
|---|
| 28 | contain only the changes since the snapshot were taken. When the snapshot is restored, <ph
|
|---|
| 29 | conkeyref="vbox-conkeyref-phrases/product-name"/> throws away that differencing image, thus going back to
|
|---|
| 30 | the previous state. This is both faster and uses less disk space. For the details, which can be complex, see
|
|---|
| 31 | <xref href="diffimages.dita#diffimages"/>. </p>
|
|---|
| 32 | <p>Creating the differencing image as such does not occupy much space on the host disk
|
|---|
| 33 | initially, since the differencing image will initially be empty and grow dynamically later with each write
|
|---|
| 34 | operation to the disk. The longer you use the machine after having created the snapshot, however, the more the
|
|---|
| 35 | differencing image will grow in size. </p>
|
|---|
| 36 | </li>
|
|---|
| 37 | <li>
|
|---|
| 38 | <p>If you took a snapshot while the machine was running, the memory state of the machine is also
|
|---|
| 39 | saved in the snapshot. This is in the same way that memory can be saved when you close a VM window. When you
|
|---|
| 40 | restore such a snapshot, execution resumes at exactly the point when the snapshot was taken. </p>
|
|---|
| 41 | <p>The memory state file can be as large as the memory size of the VM and will therefore occupy
|
|---|
| 42 | considerable disk space. </p>
|
|---|
| 43 | </li>
|
|---|
| 44 | </ul>
|
|---|
| 45 | </body>
|
|---|
| 46 |
|
|---|
| 47 | </topic>
|
|---|
