Administrators often think of a virtual machine as a single, stand-alone entity that they can move around to address their operational needs. However, a virtual machine consists of several parts, which administrators do not normally need to think about:
- Virtual hard disks, stored as files on the physical storage.
- Virtual machine snapshots, stored as a special type of virtual hard disk file.
- The saved state of the different, host-specific devices.
- The memory file for the virtual machine or its snapshot.
- The virtual machine configuration file, which organizes all of those parts and arranges them into a working virtual machine.
Each virtual machine and every snapshot associated with it must be unique, so globally unique identifiers are used. Additionally, virtual machines store and use some host-specific information, such as the path information for virtual hard disk files. When Hyper-V tries to start a virtual machine, it goes through a series of validation checks before being started. Problems such as hardware differences that might exist when a virtual machine is moved to another host can cause these validation checks to fail. That, in turn, prevents the virtual machine from starting. The administrator is left with files on the disk that take up space and are not useful.
Hyper-V in Windows Server 2012 introduces a new Import wizard that detects and fixes more than 40 different types of incompatibilities. The Import wizard walks you through the steps of addressing incompatibilities when you import the virtual machine to the new host—so this wizard can help with configuration that is associated with physical hardware, such as memory, virtual switches, and virtual processors.
Also, you no longer need to export a virtual machine to be able to import it. You can simply copy a virtual machine and its associated files to the new host, and then use the Import wizard to specify the location of the files. This “registers” the virtual machine with Hyper-V and makes it available for use. You can copy a virtual machine to an NTFS-formatted USB drive, and you can recover virtual machines in cases where the system drive fails but the data drive that stores the virtual machines is intact.
In addition to the new wizard, automation support is available. The new Hyper-V module for Windows PowerShell includes cmdlets for importing virtual machines.
To try out the Import wizard, you will need the following:
Two installations of Windows Server 2012 with the Hyper-V role installed (Hyper-V requires a computer that has processor support for hardware virtualization)
A virtual machine
A user account that belongs to the local Hyper-V Administrators group
To import a virtual machine, the wizard does the following:
1. Creates a copy of the virtual machine configuration file.
This is done as a precaution in case an unexpected restart occurs on the host, such as from a power outage.
2. Validates hardware.
Information in the virtual machine configuration file is compared to hardware on the new host.
3. Compiles a list of errors.
This list identifies what needs to be reconfigured and determines which pages appear next in the wizard.
4. Displays the relevant pages, one category at a time.
The wizard explains each incompatibility to help you reconfigure the virtual machine so it is compatible with the new host.
5. Removes the copy of the configuration file.
After the wizard does this, the virtual machine is ready to be started.