1. A method for performing data storage optimizations comprising: receiving, by a data storage optimizer on a first data storage system connected to a set of one or more other data storage systems, performance classification information, said first data storage system including a first set of one or more storage devices of a first performance classification and said set of one or more other data storage systems including a second set of one or more storage devices of a second performance classification different from the first performance classification, wherein said performance classification information indicates that storage devices of the second set are of the second performance classification; receiving, by the first data storage system from a host, a write operation to write first data to a target address of a virtually provisioned device; determining that physical storage is not currently allocated for the target address of the virtually provisioned device; and allocating a first portion of physical storage for storing the first data, the first portion of physical storage being included in a storage device of the second set having the second performance classification, wherein said target address is included in a first extent of the virtually provisioned device and said second performance classification is selected from a plurality of performance classifications in accordance with selection criteria, said selection criteria including one or more extent-level metrics characterizing workload of data operations directed to the first extent.