I/O throughput "per core" for vioperf on VMs
I have heard of several instances where customers and consultants execute vioperf showing well over 100 MB/s write and read disk throughput, yet because of having 8 or more vCPUs on their Vertica VMs they may fail to meet the recommended minimum 20 MB/s "per core" documented. Obviously in the virtual world, even the term "per core" is ambiguous as we are talking about virtual CPUs here. The end user often has no idea how many actual cores are on the underlying server or whether HT is enabled, etc.
The question is this: In the case where vioperf comes back at or just under the minimum, is the RIGHT thing to do to tell the customer to reduce the vCPU count for the VM? In other words, if they get 18MB/s "per core" write on 8 vCPUs (144 MB/s actual disk speed), should we advise they simply reboot with 4 vCPUs and rerun the test? Sure this will pass the vioperf threshold but we have not increased the disk speed and we have reduced the overall resources available on the node(s). Are we THAT sure our vioperf "per core" threshold is truly representing how well Vertica works in a virtualized environment?