Dell R610 12-Core 2x Xeon X5680 3.33GHz 64GB RAM Slow guests

[3250]

I installed Virtualbox on a windows 2016 host on a Dell R610 2xXeon with 64GB of RAM. Changing the guest CPU cores to more than 4 or RAM to more than 8GB results in almost unusable guests (Windows server 2016). Slow and up to 10 minutes boot time.
Is there something I should do to improve performance on guest machines?
Thank you in advance.

[socratis]

Remember that simple rule:

• Total CPUs for your guests ≤ Host CPUs + 1.
• Total RAM+vRAM+overhead for your guests ≤ Host available RAM + some.

By "host CPUs" we don't mean logical ones (threads), but physical ones (cores).
By available RAM, well, that's rather obvious; total - programs running and host OS.

If you need more analysis, you'd need to post the VBox.log, ZIPPED, from a complete VM run.

1. Follow a "start the VM from cold-boot" / "observe error" / "shutdown the VM" cycle.
2. With the VM completely shut down (not paused or saved), right-click on the VM in the VirtualBox Manager and select "Show Log".
3. Save only the first "VBox.log", ZIP it and attach it to your response (see the "Upload attachment" tab below the reply form).

[BillG]

Giving a vm multiple processors (beyond 2) usually results in reduced performance. It will only help if the workload is CPU bound and the processes which are running can utilize the extra CPU power. If they can't the overall effect is poorer performance.

Giving a vm more memory and more CPU power will not usually improve boot times. Giving them faster disk (such as storing the virtual disks on SSD) probably will.