The Complete
Guide to Windows Server 2008 The Complete
Guide to Windows Server 2008Check out http://www.savilltech.com/videos.html for some videos on the 2008 technologies.
In Chapter 1 table 1-2 I say Itanium has unlimited virtual image rights. This is not correct as Hyper-V is actually not supported for Itanium.
On page 1310 I briefly cover snapshots which was centered around the use of Volume Shadow Copy Service (VSS) to take a backup of a virtual machine which is not actually the process the final Hyper-V RTM uses for a snapshot which is described below.
Before we talk about snapshots lets cover a type of virtual hard disk, a
differencing disk. A differencing disk is an additional virtual hard disk file
that effectively sits on top of another virtual hard disk file and works with
the existing VHD. Any write operations are written to the differencing disk, so
no changes are made to the existing VHD. Read operations are first checked
against the differencing disk to see if updated content was written to the
differencing disk and if the content is not in the differencing disk then the
content is read from the additional VHD. This allows us to have a virtual hard
disk and then effectively freeze any changes to the existing content by adding a
differencing disk which will store any future changes.
Lets start with a snapshot of an offline virtual machine (a VM that is turned
off). When a snapshot is taken of an offline VM a differencing disk is created
to avoid any changes to the existing virtual hard disk file in a new sub-folder
of the snapshot folder for the VM with the GUID of the VM, this differencing
disk has an AVHD extension and is named with the GUID of the snapshot. In
addition a copy of the current configuration is stored in the snapshots folder
with the GUID of the snapshot.
If the virtual machine is running (online) when the snapshot is taken then two
additional files are created in a subfolder of Snapshots (named the GUID of the
snapshot) that contains two files, a .bin file which contains the contents of
the virtual machines memory and a .vsv file that contains supporting process
information. This means when you restore back to a snapshots state not only the
disk is restored to the previous point in time but also the memory of the
virtual machine and any processes that were supporting its operation.
The picture below shows the memory and process content and then the AVHD files
that are used by the snapshots.
If you create additional snapshots the process is exactly the same, a new AVHD
file is created which is a differencing file over the differencing file
currently being used since the last snapshot (confused yet :-) ). This is shown
in the picture below.
If you delete a snapshot then memory and process files are deleted and the content of any differencing disks are rolled into the preceding virtual hard disk when the virtual machine is next shutdown.
Below you will find the major code samples from the Complete Guide to Windows Server 2008.