I/O ACFS versus Huaweii Hypermetro-Mirror

one of my customers created two Test setups. One with Oracle ACFS and one with the Huaweii Hypermetro-Mirror. They used DBMS_RESOURCE_MANAGER.calibrate_io to measure the I/O Performance. The Result was that the ACFS setup showed twice the IOPS of the Hypermetro-Mirror.
The customer thinks this could be a draw, since the I/O to synchronize is done under the hood of the Hypermetro-Mirror and therefore half of the I/O could go unnoticed by the OS.

It is not exactly my core competency.
I have these questions:

1. Is the argument of the customer correct? Is the Hypermetro-Mirror performing under the hood?
2. Is calibrate_io a good tool to measure performance? I usually hear SLOB when it comes to that.
3. What other consideration besides performance would you consider useful? Fail-safe is obviously a candidate, the system is set up to be used in an hospital.

I know my questions are  a bit vague. I got the task in lack of better skilled people and I must worm myself into the topic some way. ;-)

Regards and thanks

Lothar

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