Currently, we are using SMI-S to retrieve storage information.
How does CM API compare to SMI-S? What is the need to have CM, if there is already SMI-S? What are advantages/disadvantages of CM API over SMI-S.
SMI-S is a standard API developed by SNIA (Storage Network Industry Association). It's purpose is to expose API syntax in a standard way so ideally, when you write code for one vendor, it will work for another vendor as well. In practice, this is rarely the case, but once you learn the SMI-S API, it's pretty easy to adapt to another vendor's SMI-S API.
CM REST API uses the REST Protocol (HTTP) to communicate and utilizes internal calls that perform faster, are more complete, and support multiple arrays. For instance, you can manage local users on the array with CM REST API, but you can't with SMI-S. But CM REST API is very specific to Hitachi arrays using our terminology and specific ways for managing Hitachi arrays.
Retrieving data ...