images.rst (3199B)
1 .. _disk images: 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 23 See the ``qemu-img`` invocation documentation for more information. 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