We are going through some design discussions for implementing various databases (Mongo, Cassandra, etc) on RHEL 7/8 on ESX 7. One of the design decisions is how many SCSI controllers to use. There is perceived benefit for multiple SCSI controllers but no one is able to articulate how or why this might be true. I have done some research on this found hints that in the case of Windows each virtual SCSI controller would have its own I/O queue.
(1) What, if any, are the benefits of multiple SCSI controllers for databases and why (beyond a simple it's faster)?
(2) How much of this is dependent on the operating system or operating system version?
(3) How much of this dependent on the choice of SCSI controller + driver? If the hints of multiple I/O queues are true then my guess is that this is a function of the driver.
Thanks in advance for any insight or guidance.