Hi Siva,
So, will try that option using the 5.1 version
OK, I have not yet look into 5.1 headers but from googling around it seems that VixDiskLibConnectParams struct has been updated with a thumbprint field. Further investigating this I found that especially the big vendors all face difficulties with VDDK 5.1 - not only with the thumbprint stuff but it seems that there are also threading issues. Some even use VDDK 5.0 to backup vShpere 5.1 - it was reported to work but was stated to be currently not supported by VMware.
All in all it seems that VDDK 5.1 is not there where it should be. I revisited the release notes and if you go through the "Known Issues and Workarounds" section it's a little bit deterring.
So if you invest time into the thumbprint problem be prepared to face some other show stoppers.
Maybe waiting for VDDK 5.1 Update 1 is better than investing in code that will simply be a workaround and useless once VDDK 5.1 Upate 1 is out.
But this issue in general raises a completely different question: Would it make sense to come up with a mechanism which enables the backup application to choose the VDDK version based on the vSphere version it is talking to.
Well any way, looking forward to hearing your findings