Commit 13a2e80f authored by bellard's avatar bellard
Browse files

info about VM snapshots


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@2096 c046a42c-6fe2-441c-8c8c-71466251a162
parent c88676f8
......@@ -2,6 +2,8 @@ version 0.8.3:
- Support for relative paths in backing files for disk images
- Async file I/O API
- New qcow2 disk image format
- Support of multiple VM snapshots
version 0.8.2:
......
......@@ -743,6 +743,8 @@ show USB devices plugged on the virtual USB hub
show all USB host devices
@item info capture
show information about active capturing
@item info snapshots
show list of VM snapshots
@end table
@item q or quit
......@@ -777,11 +779,18 @@ info capture
@item log item1[,...]
Activate logging of the specified items to @file{/tmp/qemu.log}.
@item savevm filename
Save the whole virtual machine state to @var{filename}.
@item savevm [tag|id]
Create a snapshot of the whole virtual machine. If @var{tag} is
provided, it is used as human readable identifier. If there is already
a snapshot with the same tag or ID, it is replaced. More info at
@ref{vm_snapshots}.
@item loadvm filename
Restore the whole virtual machine state from @var{filename}.
@item loadvm tag|id
Set the whole virtual machine to the snapshot identified by the tag
@var{tag} or the unique snapshot ID @var{id}.
@item delvm tag|id
Delete the snapshot identified by @var{tag} or @var{id}.
@item stop
Stop emulation.
......@@ -895,11 +904,14 @@ CPU registers by prefixing them with @emph{$}.
Since version 0.6.1, QEMU supports many disk image formats, including
growable disk images (their size increase as non empty sectors are
written), compressed and encrypted disk images.
written), compressed and encrypted disk images. Version 0.8.3 added
the new qcow2 disk image format which is essential to support VM
snapshots.
@menu
* disk_images_quickstart:: Quick start for disk image creation
* disk_images_snapshot_mode:: Snapshot mode
* vm_snapshots:: VM snapshots
* qemu_img_invocation:: qemu-img Invocation
* disk_images_fat_images:: Virtual FAT disk images
@end menu
......@@ -926,6 +938,57 @@ 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
snapshots 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 have to copy the full 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
@node qemu_img_invocation
@subsection @code{qemu-img} Invocation
......
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