Dell PowerVault ME5 Series Administrator's Guide

Tier setup

In general, it is best to have two tiers instead of three tiers. The highest tier will nearly fill before using the lowest tier. The highest tier must be 95% full before the controller will evict cold pages to a lower tier to make room for incoming writes.

Typically, you should use tiers with SSDs and 10K disks, or tiers with SSDs and 7K disks. An exception may be if you need to use both SSDs and faster spinning disks to hit a combination of price for performance, but you cannot hit your capacity needs without the 7K disks; this should be rare.