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diff --git a/docs/system/images.texi b/docs/system/images.texi new file mode 100644 index 0000000000..c5060348ec --- /dev/null +++ b/docs/system/images.texi @@ -0,0 +1,88 @@ +@node disk_images +@section Disk Images + +QEMU supports many disk image formats, including growable disk images +(their size increase as non empty sectors are written), compressed and +encrypted disk images. + +@menu +* disk_images_quickstart:: Quick start for disk image creation +* disk_images_snapshot_mode:: Snapshot mode +* vm_snapshots:: VM snapshots +@end menu + +@node disk_images_quickstart +@subsection Quick start for disk image creation + +You can create a disk image with the command: +@example +qemu-img create myimage.img mysize +@end example +where @var{myimage.img} is the disk image filename and @var{mysize} is its +size in kilobytes. You can add an @code{M} suffix to give the size in +megabytes and a @code{G} suffix for gigabytes. + +@c When this document is converted to rst we should make this into +@c a proper linked reference to the qemu-img documentation again: +See the qemu-img invocation documentation for more information. + +@node disk_images_snapshot_mode +@subsection Snapshot mode + +If you use the option @option{-snapshot}, all disk images are +considered as read only. When sectors in written, they are written in +a temporary file created in @file{/tmp}. You can however force the +write back to the raw disk images by using the @code{commit} monitor +command (or @key{C-a s} in the serial console). + +@node vm_snapshots +@subsection VM snapshots + +VM snapshots are snapshots of the complete virtual machine including +CPU state, RAM, device state and the content of all the writable +disks. In order to use VM snapshots, you must have at least one non +removable and writable block device using the @code{qcow2} disk image +format. Normally this device is the first virtual hard drive. + +Use the monitor command @code{savevm} to create a new VM snapshot or +replace an existing one. A human readable name can be assigned to each +snapshot in addition to its numerical ID. + +Use @code{loadvm} to restore a VM snapshot and @code{delvm} to remove +a VM snapshot. @code{info snapshots} lists the available snapshots +with their associated information: + +@example +(qemu) info snapshots +Snapshot devices: hda +Snapshot list (from hda): +ID TAG VM SIZE DATE VM CLOCK +1 start 41M 2006-08-06 12:38:02 00:00:14.954 +2 40M 2006-08-06 12:43:29 00:00:18.633 +3 msys 40M 2006-08-06 12:44:04 00:00:23.514 +@end example + +A VM snapshot is made of a VM state info (its size is shown in +@code{info snapshots}) and a snapshot of every writable disk image. +The VM state info is stored in the first @code{qcow2} non removable +and writable block device. The disk image snapshots are stored in +every disk image. The size of a snapshot in a disk image is difficult +to evaluate and is not shown by @code{info snapshots} because the +associated disk sectors are shared among all the snapshots to save +disk space (otherwise each snapshot would need a full copy of all the +disk images). + +When using the (unrelated) @code{-snapshot} option +(@ref{disk_images_snapshot_mode}), you can always make VM snapshots, +but they are deleted as soon as you exit QEMU. + +VM snapshots currently have the following known limitations: +@itemize +@item +They cannot cope with removable devices if they are removed or +inserted after a snapshot is done. +@item +A few device drivers still have incomplete snapshot support so their +state is not saved or restored properly (in particular USB). +@end itemize + |