This is a pretty decent guide for setting the growth size on the CPGs
https://www.youtube.com/watch?v=zgVXWjq3W_cBasically - RAID Data * Number of disks / Data plus parity.
So for R5 3+1 this is 3 * Disks in that class (48 in my case) / 4 which works out to 36GB.
We only have 3 CPGs and we ran that math on all 3 before we started creating volumes and we see all the disks participate in IO.
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The only problem with doing this kind of thing is that very rarely do systems remain static. E.g more disks and nodes get added over time so the numbers will change and if you want to maintain these, then you'll end up micromanaging the system, which isn't really 3PAR's design goal.
Changing a few growth numbers and running Tunesys is hardly micromanaging. How often do you really add disks? Once a year? Once every few years? It's a minor thing to change to get the best performance out of all the drives you've paid for.