Depending on the version of ONTAP you have installed you can probably take advantage of aggregate level deduplication so i don't think there would be much advantage from a storage efficency perspective if you were to create a single volume or multiple volumes. Creating multiple volumes based on workloads and application (within reason) would seem logical given you could apply a QoS policy to those volumes to limit potential performance impact.
It might also depend on your DR strategy, rate of change, available bandwidth for snapmirror to your DR site and your RPO\RTO per application\datastore when considering how to provision the storage. If you have applications that require independant DR failover (from a storage perspective) of other VM's within a volume\vsphere datastore, then you may require multiple vservers\volumes rather than one large volume. Just some thoughts to consider.
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