If the above values are for two different datastores, over-provision rate can be calculated (in simple terms) as below -
Datastore-1 --> (Provisioned/DataTotal)*100 --> (6422/3400)*100 = 188 percent over-provisioned
Datastore-2 --> (8654/3200)*100 = 270 percent over-provisioned
Since the information is not clear, I'm assuming 'DataTotal' to be the size of the datastores.
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Cheers,
Supreet