clarification on StoragePoolsCollection

Regarding "StoragePools" vs {StoragePoolId} = the CollectionName is generally plural, to refer to multiple resource instances, where the {instanceId} is singular in the reference. This is the general pattern throughout Redfish and Swordfish.

For the emulator, there is an "index.json" file in every level of the system; for the "StoragePools", it will be for the Collection itself. For the StoragePools/{StoragePoolId} level, it will be for the instance of a specific StoragePool.

In RF and SF, there are two ways to use the Collection notation. One is, effectively, an array vs a collection. In this format: Collection (StoragePool.StoragePool), this is an array. If in this format, StoragePoolCollection.StoragePoolCollection, it is a resource Collection. Resource collections are used when the number of objects may change, and also when the set is likely to be large. (Arrays are used when a simpler construct may suffice.)

For the question related to "why have multiple StoragePool Collections". Large storage systems can have 1000's of drives, allocated into many storage pools. For some systems, these are also hierarchical. For example, a file system may have pools of file systems created on top of pools of block storage.
For NVMe environments, this is also true. NVMe devices using endurance groups are created on top of NVM sets; these are modeled using storage pools. We have examples of these configurations available at storagemockups.com