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923e9311 | 1 | .. _disk images: |
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2 | |
3 | Disk Images | |
4 | ----------- | |
5 | ||
6 | QEMU supports many disk image formats, including growable disk images | |
7 | (their size increase as non empty sectors are written), compressed and | |
8 | encrypted disk images. | |
9 | ||
10 | .. _disk_005fimages_005fquickstart: | |
11 | ||
12 | Quick start for disk image creation | |
13 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
14 | ||
15 | You can create a disk image with the command:: | |
16 | ||
17 | qemu-img create myimage.img mysize | |
18 | ||
19 | where myimage.img is the disk image filename and mysize is its size in | |
20 | kilobytes. You can add an ``M`` suffix to give the size in megabytes and | |
21 | a ``G`` suffix for gigabytes. | |
22 | ||
c5ba6219 | 23 | See the ``qemu-img`` invocation documentation for more information. |
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24 | |
25 | .. _disk_005fimages_005fsnapshot_005fmode: | |
26 | ||
27 | Snapshot mode | |
28 | ~~~~~~~~~~~~~ | |
29 | ||
30 | If you use the option ``-snapshot``, all disk images are considered as | |
31 | read only. When sectors in written, they are written in a temporary file | |
32 | created in ``/tmp``. You can however force the write back to the raw | |
33 | disk images by using the ``commit`` monitor command (or C-a s in the | |
34 | serial console). | |
35 | ||
36 | .. _vm_005fsnapshots: | |
37 | ||
38 | VM snapshots | |
39 | ~~~~~~~~~~~~ | |
40 | ||
41 | VM snapshots are snapshots of the complete virtual machine including CPU | |
42 | state, RAM, device state and the content of all the writable disks. In | |
43 | order to use VM snapshots, you must have at least one non removable and | |
44 | writable block device using the ``qcow2`` disk image format. Normally | |
45 | this device is the first virtual hard drive. | |
46 | ||
47 | Use the monitor command ``savevm`` to create a new VM snapshot or | |
48 | replace an existing one. A human readable name can be assigned to each | |
49 | snapshot in addition to its numerical ID. | |
50 | ||
51 | Use ``loadvm`` to restore a VM snapshot and ``delvm`` to remove a VM | |
52 | snapshot. ``info snapshots`` lists the available snapshots with their | |
53 | associated information:: | |
54 | ||
55 | (qemu) info snapshots | |
56 | Snapshot devices: hda | |
57 | Snapshot list (from hda): | |
58 | ID TAG VM SIZE DATE VM CLOCK | |
59 | 1 start 41M 2006-08-06 12:38:02 00:00:14.954 | |
60 | 2 40M 2006-08-06 12:43:29 00:00:18.633 | |
61 | 3 msys 40M 2006-08-06 12:44:04 00:00:23.514 | |
62 | ||
63 | A VM snapshot is made of a VM state info (its size is shown in | |
64 | ``info snapshots``) and a snapshot of every writable disk image. The VM | |
65 | state info is stored in the first ``qcow2`` non removable and writable | |
66 | block device. The disk image snapshots are stored in every disk image. | |
67 | The size of a snapshot in a disk image is difficult to evaluate and is | |
68 | not shown by ``info snapshots`` because the associated disk sectors are | |
69 | shared among all the snapshots to save disk space (otherwise each | |
70 | snapshot would need a full copy of all the disk images). | |
71 | ||
72 | When using the (unrelated) ``-snapshot`` option | |
73 | (:ref:`disk_005fimages_005fsnapshot_005fmode`), | |
74 | you can always make VM snapshots, but they are deleted as soon as you | |
75 | exit QEMU. | |
76 | ||
77 | VM snapshots currently have the following known limitations: | |
78 | ||
79 | - They cannot cope with removable devices if they are removed or | |
80 | inserted after a snapshot is done. | |
81 | ||
82 | - A few device drivers still have incomplete snapshot support so their | |
83 | state is not saved or restored properly (in particular USB). | |
84 | ||
85 | .. include:: qemu-block-drivers.rst.inc |