1. A method for metadata management in a storage system, the storage system configured for supporting sub-LUN tiering, the method comprising: providing a least recently used (LRU) queue of a specific size, the LRU queue configured for caching metadata for a specific number of sub-LUNs; determining whether the metadata for a particular sub-LUN is cached in the LRU queue when the particular sub-LUN is being accessed; updating the metadata for the particular sub-LUN and moving the updated metadata to the head of the LRU queue when the metadata for the particular sub-LUN is cached in the LRU queue; inserting the metadata for the particular sub-LUN to the LRU queue when the LRU queue is not full and the metadata for the particular sub-LUN is not cached in the LRU queue; replacing a last entry in the LRU queue with the metadata for the particular sub-LUN when the LRU queue is full and the metadata for the particular sub-LUN is not cached in the LRU queue; and identifying at least one frequently accessed sub-LUN for moving to a higher performing tier in the storage system, the at least one frequently accessed sub-LUN being identified based on the metadata cached in the LRU queue.