With midrange arrays rapidly closing the gaps that exist between them and monolithic arrays, certain key differences remain:
Mainframe support. Midrange arrays usually don't support either mainframe ESCON or FICON connectivity, but this is changing because EMC and IBM offer FICON connectivity on their upper-end midrange arrays.
Skill sets. Administrators generally need to be more technically proficient to manage a monolithic array.
Replication services. Monolithic arrays support highly specialized replication features, such as consistency groups to ensure that a consistent point-in-time copy of application data exists before any further writes are written to the source data.
Availability and reliability. Monolithic arrays provide higher availability and reliability for the most demanding applications.
Known issues. Microcode bugs appear even in the best of arrays, especially those used in heterogeneous environments. Bugs in monolithic arrays tend to be better documented, easier to identify and corrected faster than those in midrange code.
--JEROME M. WENDT