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post #91 of 99 Old 07-17-2014, 08:46 AM
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Originally Posted by ncarty97 View Post

So, can I just change the number of cores and memory in the ESXi virtual machine setup? Will the OS just recognize it or does this kind of thing require me to re-install the OS?

Thanks!
The short answer is you can.

The long answer is this is not advisable. In terms of the guest OS, it's as if you are swapping out the CPU and thus can introduce instability. In addition, adding more cores to the VM does not increase VM performance.

I would spend some time looking at the CPU utilization on both the guest OS and on the host. I imagine disk latency and memory pressure is a much larger concern than CPU performance.
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post #92 of 99 Old 07-17-2014, 08:50 AM
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Thanks!

I haven't had any performance issues so far, just preparing as we'll be using Quickbooks more often going forward (started a new business last month). The OS runs on an SSD, so disk latency shouldn't be much of an issue.

I suppose I can back up the VM, change the cores and see if it produces any problems. If it does, then I can just restore and decide later if its going to be worth it to re-install the OS. Upping the memory shouldn't cause any instability I would think.

Thanks again.
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post #93 of 99 Old 07-17-2014, 09:13 AM
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Quote:
Originally Posted by Dysfnctnl85 View Post
The long answer is this is not advisable. In terms of the guest OS, it's as if you are swapping out the CPU and thus can introduce instability. In addition, adding more cores to the VM does not increase VM performance.
That conclusion doesn't follow from the link you posted. They were testing a fixed number of cores in different #sockets * #corespersocket configurations. All else being equal, adding more cores will increase vm performance in cpu-bottlenecked tasks.

Your "thus can introduce instability" claim is FUD. The whole point of virtualization is being able to adjust the allotted resources as needed. Windows Server VMs on ESX have supported hotplugging ram and cpu since 2003.
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post #94 of 99 Old 07-17-2014, 09:40 AM
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That article is more about the difference between choosing 4 sockets with 1 core each (for example) rather than 1 socket with 4 cores. Nothing at all to do with a general performance increase when adding cores, which will indeed increase if more cores are added (hyperthreaded cores not as much).

In any case, I have added/removed cores on all sorts of VMs and never encountered any issue.
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post #95 of 99 Old 07-17-2014, 09:42 AM
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Thanks guys. A short follow up, can someone give me a quick primer on cores vs sockets? I think I get the general concept, but I'm not sure. Thanks
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post #96 of 99 Old 07-17-2014, 10:23 AM
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Quote:
Originally Posted by ncarty97 View Post
Thanks guys. A short follow up, can someone give me a quick primer on cores vs sockets? I think I get the general concept, but I'm not sure. Thanks
A socket is a whole physical processor. A core is an additional execution unit on a physical processor.

VMware treats them virtually the same from a performance aspect. The distinction is more for OS and application software vendor licensing. For example, Microsoft desktop OSes have been traditionally limited to two physical CPUs. You can have many more cores per CPU, so to maximize your system utilization/performance you would use a combination of sockets and cores.
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post #97 of 99 Old 07-17-2014, 10:24 AM
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Part of it was licensing, where software would be licensed "per socket". So if you had a 2 socket system with 4 cores each, you could present a single socket CPU with 8 cores to the VM, and only have to pay for one license.

That article linked specifies that if you can, give VMs 8 single core sockets instead of a single socket with 8 cores (for example).
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post #98 of 99 Old 07-17-2014, 11:40 AM
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Originally Posted by EricN View Post
That conclusion doesn't follow from the link you posted. They were testing a fixed number of cores in different #sockets * #corespersocket configurations. All else being equal, adding more cores will increase vm performance in cpu-bottlenecked tasks.

Your "thus can introduce instability" claim is FUD. The whole point of virtualization is being able to adjust the allotted resources as needed. Windows Server VMs on ESX have supported hotplugging ram and cpu since 2003.
It's not a question of whether or not VMWare supports it, it's about the guest OS.

It's not FUD. Modifying the hardware running Windows can result in HAL issues. I could not in good conscience tell OP to do this and as a result OP has to repair Windows -- that's not fun for anyone. It's just a risk worth noting. I've successfully altered cores and vCPUs without issues in the past, but I've also had bad experiences and needed to perform repair installs of Windows. YMMV.

The article discusses NUMA architecture, which is important in understanding how the hypervisor treats vCPUs and virtual sockets. VMWare best practices documentation discusses this in detail and warns of overcommitting vCPUs. Adding cores or vCPUs to a guest OS does not guarantee increased performance and can negatively impact the performance of multiple VMs by creating contention among them.

Monitor the existing VM and find its pain points. Adjust accordingly.
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post #99 of 99 Old 07-19-2014, 08:43 AM
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I had heard assigning all VMs a single virtual core in esxi allows it to allocate virtual cores as necessary rather than needing manual reassignment

Is that correct?
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