fio tool to size BW, throughput and latency Oracle, Postgres , Mysql workloads

I am trying to run fio <https://fio.readthedocs.io/en/latest/fio_doc.html> and I cannot get the right combination of commands for below systems I am sizing for.

1. OLTP iops ,bw, latency are important to size correctly to avoid latency. but rate= parameter doesn't seem to work.
2. DSS Should I just focus on iops and bw here
3. Mixed How do I play with fio to get the right set of commands using rwmixread/write?

Few questions:
- Do I have to ensure all the disks are created in the target before I run
the tests?
- Can you please share your examples of fio commands for 1,2,3 above

• How to set the numjobs correctly?

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Cheers,
Kunwar

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