x5-2 1/8th putting io hard limit on one of pdbs and WBFC as a bonus q

Hi,
  we are on x5-2 1/8 (3storage + 2 DB nodes) rack, GI + RDBMS is 12.1.0.2 . Trying to put IO constraints on one of PDBs like 80% hard limit for getting Cell I/O performance .
As far as I can tell only two options there : 1 Performance_profiles (inherited from CDB ) Questions:

• do I have to include all other DB (cdbs+PDBS) in IORM plan even if I dont care about them in terms of I/O performance ? 2. shares + utilization_limit same question as above ?

What whould You recommend as a best solution in such way stated problem (throttling I/O of one PDB only in terms on real hard limit like 80% I/O capacity of the cell ) .

Bonus question :
In terms of switching into write back cache in rolling fasion , does the 3 cell nodes still allows me to go in rolling mode without crashing the running instances ?

Regards
GG

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