[vbox-dev] About .SAV file created by snapshots

Frank Mehnert frank.mehnert at oracle.com
Thu Oct 11 00:37:39 PDT 2012


On Thursday 11 October 2012 07:32:31 prabhjeet kaur wrote:
> How one can read the .SAV file created by snapshots. In which form
> snapshots save the details regarding difference from the last snapshot,
> memory details, etc... Where the API of snapshot is available.

a .sav file contains always the *complete* state of the guest at a certain
point in time. It does *not* contain any information stored on external
devices like virtual disks. When a snapshot is created, a .sav file is
created containing the VM state which is required to restore the guest
state for that time and a new differential disk image is created for each
virtual disk (which is not attached in some special mode to prevent that).
From now on, guest disk write requests go to the differential image. When
you restore a snapshat, the differential image is removed so all changes
to the disk after the snapshot was created are lost.

A .sav file is created using the SSM (saved state manager) code. You will
find the API in include/VBox/vmm/ssm.h and src/VBox/VMM/VMMR3/SSM.cpp.

Kind regards,

Dr.-Ing. Frank Mehnert | Software Development Director, VirtualBox
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