The user cache on VMAX systems is usually pretty large, and all of it can be used for reads.  It uses an LRU algorithm to keep frequently read data in cache so we can get read hits even on random IO.  Configuration information is also kept in cache (meta data) separate from the user data, but both areas are accessible by all directors.  There is more detail in the product guide. The older guides had a lot more detail on IO flow, but a quick search didn't come up with the old guides. [URL]  Chapter 3 of this DMX3 manual has the detail on IO flow, which is pretty much the same as VMAX at the high level.  [URL]
In VNX/Clariion environment we got Active/Passive ( SPA/SPB or Primary DM/Seconday DM ) mode operation, when Primary fails, Standby takes control of all luns/FS and process IO accordingly..   But in VMAX/DMX architecture why do we have Active/Active mode operation to serve workloads ?  Friend of mine referenced , that Cache plays a big role in VMAX/DMX architecture to serve IOPS. Where Cache has set of tables for each THIN device and performs mapping between Frond end IO modules and Back end IO modules. I am not sure if that is the method followed to serve IOPS in VMAX/DMX.  Can experts clarify ?
Front end IO modules/Back end IO modules and Cache usage dependancy