Once again I’ve run into an information technology director faced with acquiring software for storage that was licensed on a per-terabyte basis. Like others I’ve talked to in that situation, he made his decision based on that charge and not by taking into full consideration what he needed. The cost-per-terabyte charge can be so large that it has an impact on efficient storage operations.
The cost-per-terabyte charge applied in storage varies depending on the product and the vendor. Vendors are not even consistent from product to product on the charges. A few of the different ways they are represented to their customers illustrate this frustrating point:
Per terabyte of managed capacity is a common charge for storage management software. Unfortunately, vendors definite managed capacity differently.
Rest of article: http://itknowledgeexchange.techtarget.com/storage-soup/per-tb-licensing-changes-behavior-impacts-efficiency/