VMware vSphere SDKs and Tools 8.0

8.0 7.0 6.7 6.5

Virtual Disk Development Kit

This SDK is most frequently used to implement backup and restore applications. This section is a walk-though of code to restore a virtual machine.
The Virtual Disk Development Kit (VDDK) is a set of libraries and utilities that enable software developers to create applications that can access and manipulate virtual disks used for storage by products such as vSphere, Workstation, and Fusion. VDDK is a valuable tool for developers of storage and backup applications.
VDDK provides APIs for backup and recovery, cloning, and other operations on virtual disks. With VDDK, developers can create applications that perform backup and restore operations for virtual machines, as well as applications that create clones or snapshots of virtual disks. VDDK also includes utilities for converting virtual disks between different formats and for creating virtual disks from scratch.

Safekeeping – a VDDK Use Case

Based on VDDK, Safekeeping is a "proof of concept" application to demonstrate backup and restore of vSphere VMs, vApps, and first-class disk. You can find its source code on Github, as linked from the developer.broadcom.com SDK landing page for VDDK. This section focuses on
RestoreVm.java
, a source code module that recovers a VM previously saved by the
BackupVm.java
 module. 
safekeeping backup vm:myTestVM
safekeeping restore vm:myTestVM
After package and interface imports, class
RestoreVm
 extends method
AbstractRestoreFcoWithDisk
, which in turn extends method
AbstractRestoreFco
 for restoring a first class object (FCO) but with disk, as in a vSphere VM. (A vApp is an FCO that includes VMs but not disk.)
RestoreVm
 must be passed a VIM connection, user-specified command options, and a log file.
The
checkOptions
 method parses passed-in options, including (if specified) VM name, parent vApp, data center, resource pool, datastore, and storage profile. If the destination VM folder cannot be restored to,
RestoreVM
 uses a different location.
Snapshot is a typical operation for both backup and restore. The
createSnapshot
 method takes a vSphere snapshot so the VM can continue running while being restored, and also to quiesce the virtual disk while it is being replaced. If a snapshot is unnecessary because the VM does not exist, snapshot is skipped.
If the VM is being restored because it no longer runs, the
destroy
 method deletes the old VM so it does not conflict with the VM to be restored.
The
disksMapping
 method is one of the most complicated in
RestoreVM
. It needs to know the number of disks to restore, the storage profile of disks, and the location of disk data in the backup. This information comes from the
managedInfo
 object, combined with the generated
profile
 object.
Once virtual disks are correctly mapped, they are restored by the
disksRestore
 method. This could take a lot of time, so the
final
 loop blocks until disks are restored.
If a failed VM was not deleted, the
manageExistingFco
 method deals with naming conflicts between the pre-existing VM and the VM to be restored. The VM might be part of a vApp, which allows duplicate names. If the pre-existing VM is powered on, the backed-up VM cannot be restored. With duplicate names, the user can be given a chance to rename VM to be restored.
The
networksMapping
 method determines what networks the backed-up VM used for each virtual NIC, and attempts to reformulate them using existing networks.
Finally the
powerOn
 method starts up the restored VM so it can be configured. A VM can be powered on before the Guest OS is ready to run.
The
reconfig
 method configures the VM based on profiles of its virtual disks and networks determined above. Configuration may be interrupted by a fault. Similar
reconfigDisk
 and
reconfigNetwork
 methods take care of disk backing and network backing for the VM to be restored. The
removeSnapshot
 methods cleans up the snapshot previously created.
Finally the
restore
 method, the main restore function, puts this all together. It retrieves the restore profile and calls snapshot, start-access,
disksRestore
, and end-access in an if statement. This is where the C++ functions in VixDiskLib get called (start and end access prevent vMotion during restore).
 if (createSnapshot(rar) && startVddkAccess(rar, jvddk) && disksRestore(rar, jvddk) 
                         && endVddkAccess(rar, jvddk)) {
    final String st = rar.getFcoToString() + " Restore Success - start cleaning";
 }
The restored VM could either be newly created with the
restoreByCreate
 method, or recovered with import of virtual disk data by the
restoreByImport
 method. It is the
restoreMetadata
 method that decides which. The
restoreManagedInfo
 method takes care of items managed by vCenter Server, such as folder groupings and resource pools.

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