Hi vJJ, appreciate your input.
Let me add some details about my datastore. Prior to the conversion I've got a little over 1TB free out my datastore's total capacity of 1.22TB. Even though the conversion failed, it took up 280GB which is the total space I thick provisioned for volumes C & D. Eventually the free space on my datastore is now 720GB. Are you able to tell me how can I free up that space again? As soon as I sort that one out, I will retry the conversion this time using thin provisioning for the failed volume. The defragmentation went well by the way. Thanks