Auto-Tiering is used by many arrays to move data across different tiers of disk. Typically Tiers are set up in a similar fashion to this, but may vary:
- Tier 1 - SSD or SAS/FC Drives with SSD Cache
- Tier 2 - SAS/FC 10k-15k drives
- Tier 3 - SATA, 7200 rpm drives
When auto-tiering is enabled, the array will moved data accross the different drive types/pools/tiers based on access patterns, etc. Primary purpose is generally to increase performance and reduce the resources of attmepting to do this manually.
It attempts to move data to the faster tiers when it needs to be accessed. Data that is mostly inactive is moved to slower storage.
Load balancing is generally for your paths. This is set by a policy such as round robin, where your data is "balanced" accross the available ports/paths. This is for balancing your SAN traffic across different switch ports and front end ports on the array.
SAN storage arrays require continual redesign and tuning to ensure that I/O is load balanced across all storage array paths. To meet this requirement, distribute the paths to the LUNs among all the SPs to provide optimal load balancing. Close monitoring indicates when it is necessary to manually rebalance the LUN distribution. Some vendors will also "auto load balance" between controllers for individual luns.
Terminology can vary slightly from Vendor to Vendor. Is there a particular array that you are inquiring about? I can update my reponse to be more detailed towards to particular product/vendor.