Optimizing server hardware for performance (BIOS settings)

[bolsen]

VMware and the community have done a great job documenting the best practices for optimizing applications running in a virtual environment.  One area they haven't done so well in, however, is best practices in optimizing hardware.

Let me explain.

Yes - VMware is clear on the fact that any Virtualization assists should be enabled in the server bios.  However, there are many other options which affect performance.  IBM claims there can be as much as a 20% improvement in performance by disabling the processor hardware prefetcher (enabled is the default).  Dell has an option to configure RAM in a high bandwidth mode (more bandwidth is good, right?!).  Of course, HP recommends you keep all default values, but don't forget to disable power saving features.

The challenge of all this is the ability to tune a server for small workloads vs a high work loads.  Should I tune hardware differently for 1 or 2 VMs than one running 25 - 30?  At what point do these other hardware options cause performance problems?

I understand there's no easy way to answer these questions and it always depends on the workload and configuration (i.e. benchmarking will confirm the results).  However, it would be nice if VMware could give some feedback on these settings.  Perhaps it's as easy as running the same VMmark test with CPU caching enabled, just to show the difference?

Thoughts?

[SuperSpike]

This is a great question. I'm trying to find out this same information myself. We just got a bunch of new HP BL460c G7s and I'm preparing to install ESXi 4.1.

I posed the question to HP Support and they came back with a few recommendations, particularly around the HW Prefetcher and Adjacent Sector Prefetch settings. I was surprised when HP Support recommened both be set to Disabled. However, they did not cite a reference at all when making this recommendation. I'm going to respond asking for references, and will advise when I hear back.

[bolsen]

Correct, most vendors will suggest you turn off the hardware and adjacent sector prefetch, especially for pre-nehalem Intel procs. Nehalem and newer have improved fuctionality to work with over agressive prefetching, thus it's not as important to disable (i.e. you can leave it on).