You cannot get write access to a virtual disk that is in active use. For a full restore, you first must ensure that the virtual disk is not in use by halting the parent virtual machine, then performing the “power off” sequence. The following code sample demonstrates how to “power off” a Virtual Machine:
// At this point we assume that you have a ManagedObjectReference to the VM - vmMoRef. // Power on would need a ManagedObjectReference to the host running the VM - hostMoRef. ManagedObjectReference taskRef = serviceConnection.powerOffVm(vmMoRef);
With SAN transport mode, you must create a snapshot of the virtual machine before virtual disk restore. See Creating a Snapshot. If at restore time the virtual machine had a pre-existing snapshot, you must delete it, otherwise SAN mode restore will fail. For other transport modes, the restore snapshot is optional.
With a VVol datastore, the restore snapshot is forbidden when restoring to the parent (backing disk). A null MoRef is allowed as of vSphere 6.0 to minimize code changes when applications restore to a VVol datastore. To get the unique ID of a VVol object in the MOB (managed object browser) click VirtualMachine > Config > Hardware > Device (VirtualDisk) > Backing.
Summary of restore snapshot requirements summarizes the snapshot requirements.
| NBDSSL | HotAdd | SAN | |
|---|---|---|---|
| Non-VVol datastore | A snapshot is optional. If a snapshot is used, writing to either the leaf disk or the parent disk is supported. If writing to the parent disk, the snapshot must be reverted and then deleted. | A snapshot is required. Writing to the leaf disk is not supported, and writes must only go to the base disk. The snapshot must be reverted and then deleted. | |
| VVol datastore | A snapshot is optional. If a snapshot is used, writing must be to the leaf disk only. | Not applicable, because SAN transport is not supported on VVol datastores. | |
In this phase you use VixDiskLib to reload contents of the Virtual Disk, so the following code is C++ not Java:
// At this point we assume that you already have a VixDiskLib connection to the server machine.
uint8 mybuffer[some_multiple_of_512];
int mylocalfile = open("localfile", openflags); // Contains backup copy of virtual disk.
read(mylocalfile, mybuffer, sizeof mybuffer);
vixError = VixDiskLib_Open(srcConnection, path, flags, &diskHandle);
VixDiskLib_Write(diskHandle, startsector, (sizeof mybuffer) / 512, mybuffer);
With SAN transport mode, you must revert-to and delete the snapshot. If you forget the snapshot revert, snapshot delete will fail due to CID mismatch, so the virtual machine cannot be powered on. If you forget the snapshot delete, the extraneous snapshot will cause restore problems for subsequent backups.
