max upload part number in one multipart upload.

5GB, max object size in single upload.

map from cloud vendor name to a map, which is used to map from storage class name to internal tier.

map from cloud vendor name to a map, which is used to map from internal tier to it's storage class name.

map from a specific tier to an array of tiers, that means transition can happens from the specific tier to those tiers in the array.