I don't agree 100% with what Trireed is saying. I believe matching the spindle counts between node pairs is more important than matching the shelf counts, I feel this way primarily because after 2 shelves, they become daisy chained off each other.
If node 0 and 1 share 6 cages, 3 cages on one loop, and 3 cages on the other loop, with 4 drives per cage for a total of 24 drives.... and you want to add 2 more nodes, with 2 more cages, 12 drives per shelf make for a balanced workload after you systuned. 24 spindles on each node pair, 12 drives per 4 loops.
Back to your main question... ideally, you want an even balance of NL and SAS across your nodes for best performance. Yes you can avoid doubling up your SAS spindle counts, IF you dont mind a gruesome involved process of rebalancing your data multiple times to free up SAS spindles to move around. You will want to co-plan this with 3PAR sales engineers/support. The easiest thing I would suggest is install your NL drives equally balanced between all 4 nodes. Create a new NL only CPG, Dynamic Optimize ALL of your LUNs to the NL... work with support to confirm that the SAS drives to be moved are free and clear of data, have them run through the commands to remove those spindles from the hardware config, move them to the new node pair, and add that hardware into the config. At that point you could us AO policies to move your hot data to SAS, or you can DO complete VVs back.
_________________ Richard Siemers The views and opinions expressed are my own and do not necessarily reflect those of my employer.
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