As a general rule, set an extent size of either 256 MB or 512 MB for Easy Tier enabled  configurations. With these extent sizes, the maximum configurable capacity for an IBM  Spectrum Virtualize/Storwize system is 1 PB and 2 PB. For systems with larger capacity  requirements, bigger extent sizes must be used. Special considerations apply to Data  Reduction Pools (DRP) as discussed in “Easy Tier and remote copy considerations” on  page 324. For DRP the extent size recommendation is 4 GB or larger. IBM Easy Tier is an algorithm that has been developed by IBM Almaden Research and made  available to many members of the IBM storage family, such as the DS8000, IBM Spectrum  Virtualize, and Storwize products. The DS8000 is the most advanced in Easy Tier  implementation and currently provides features that are not yet available for IBM Spectrum  Virtualize and Storwize technology, such as Easy Tier Application, Easy Tier Heat Map  Transfer, and Easy Tier Control.  Before V7.3, IBM Spectrum Virtualize/Storwize had basically only two tiers and no  autorebalance feature was available. For this reason, when using external controllers with  more advanced tiering capabilities like the DS8000, the preferred practice was to enable  tiering at the backend level and leave IBM Spectrum Virtualize/Storwize Easy Tier disabled.  With V7.3 and the introduction of the autorebalance function, Easy Tier can be effectively  enabled at the IBM Spectrum Virtualize/Storwize systems level. However, consider that IBM  Spectrum Virtualize is not aware of the tiering functions of an external controller, and vice  versa. So each tiering function makes its decisions independently. What you need to avoid is  rebalance over rebalance because this situation can cancel any performance benefits. Consider the following two options: Chapter 7. IBM Easy Tier function  323 External controller tiering considerations GLYPH<SM590000> Easy Tier is done at the IBM Spectrum Virtualize/Storwize level: a. In this case, complete these steps at the backend level: i. Set up homogeneous pools according to the tier technology available. ii. Create volumes to present to IBM Spectrum Virtualize/Storwize from the  homogeneous pool. iii. Disable tiering functions. b. At an IBM Spectrum Virtualize/Storwize level, you need to complete the following  actions: i. Discover the MDisks provided by the backend storage and set the tier properly. ii. Create hybrid pools that aggregate the MDisks. iii. Enable the Easy Tier function. GLYPH<SM590000> Easy Tier is done at the backend level.  a. In this case, complete these actions at the back-end level: i. Set up hybrid pools according to the tier technology available. ii. Create volumes to present to IBM Spectrum Virtualize/Storwize from the hybrid  pools. iii. Enable the tiering functions. b. At IBM Spectrum Virtualize/Storwize level, you need to complete the following actions: i. Discover the MDisks provided by the backend storage and set the same tier for all. ii. Create standard pools that aggregate the MDisks. iii. Disable the Easy Tier function.