dlm1975
Contributor
Contributor

How do I justify a 4 CPU requirement?

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I have a virtualization candidate which the app owner is telling me requires 4vCPUs. Do you know what info he should provide to justify this requirement? I've suggested running perfmon on the box to get cpu and mem metrics. Does anyone have any other suggestions?

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khughes
Virtuoso
Virtuoso

I would run the perfmon and see what you get out of it. If the stats show it really needs 4 cpus or the software requires 4 cpu's .... it might just be better off staying as a physical box. Some things just don't virtualize unless you have a large esx host that could run a 4 vCPU VM well.

-- Kyle "RParker wrote: I guess I was wrong, everything CAN be virtualized "

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madcult
Enthusiast
Enthusiast

I would ask him for the minimum requirements of the software vendor.

You could lose support for this software if hardware is undercut.

Perfmon is really the only thing you can run, and then, in my opinion, the only statistic that matter is Processor Queue Depth. If the processor queue depth is constantly high, then multiple CPU's would aide in the servers performance. Just high CPU utilization doesn't mean that the server is processor bound - unless that high CPU utilization is across all 4 of its existing physical CPUs.

Wimo
Hot Shot
Hot Shot

The scare tactic of explaining that a 4 vCPU VM must wait for 4 physical CPUs to be available on every cycle, and therefore can run slower than 1 or 2 vCPUs, works for us on occasion.

Or, if possible, propose a test to see which way performs better. The change from 2 to 4 only takes a one minute shutdown after all.

It is almost impossible to convince anyone used to multiprocessors that they might actually be better off with 1. For that reason, I would bet we have at least 50% more vCPUs in our environment than are needed.

It is a tough battle - good luck!

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khughes
Virtuoso
Virtuoso

I would run the perfmon and see what you get out of it. If the stats show it really needs 4 cpus or the software requires 4 cpu's .... it might just be better off staying as a physical box. Some things just don't virtualize unless you have a large esx host that could run a 4 vCPU VM well.

-- Kyle "RParker wrote: I guess I was wrong, everything CAN be virtualized "
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