VMAX-3 Track Size 128k where it comes from?

Hi,

I want to learn, for what reason VMAX-3 has 128k as track size. My question is:

In VMAX-3 what has caused a track size to be 128k? Is it logical track size that is defined by Microcode that runs in VMAX-3 or is it due to PD's actual track size(PD's that are shipped in VMAX-3). If it is due to Microcode design then what is the advantage of having 128k track size. How it was in earlier VMAX arrays and reason for transition into 128k? Any input will help.

Thanks,

--ranjan