CPU Configuration and slow VMs on Mac Mini i5

[MacSS]

I have typically always used a quad core mac mini for my ESXI machine, but in this one particular case, I used a dual-core 2.53GHz with 8GB or RAM. With these specs, I thought it would be wise to only install two VM on this machine, versus the typical 4 that I do on the i7 Mac Minis.

The issue that I am having on the 2.53 i5 machine is that one of the two VMs don't seem to by utilizing the CPU to it's fullest potential when needed, and at times, only consumes about 1-1.5GHz of the CPU when I believe it should be allocating double that. The result is a slow VM at times.

I am running ESXI 5.5 on the machine, and for both of the VMs on it, have configured them to have 1 Virtual Socket and 2 Virtual Cores for the CPU. Is there something I am missing?

Gian

[MacSS]

OK, so here is an update that will hopefully spark a reply from someone who has been through this. After checking all the settings, and not finding anything, I shut down both of the VMs to the system, and rebooted the ESXi. Once rebooted, I started both the VMs back up.

After doing so, they both were fast and working as they should. After about an hour or two, I began to notice the performance degregation again. I then repeated the steps of shutting down the OS on both the VMs, rebooting the ESXi, and turning the VMs back on, and once again, back to normal.

How could everything work after reboot, then get really slow? I checked the main CPU, and it was only using about 25%-50% at times, so it wasn't peaking.

Anyone have an idea of what I should do next other than dumping the whole machine?

[Darius Davis]

How much RAM do you have allocated to the two VMs, and what OS do you have running inside them?  If there is a period of reasonable performance and a decline after some running time, my guess is that something is starting to swap to disk.  It might be the guest OS that's swapping (if there is too little RAM available inside the VM) or it might be ESXi itself swapping if you've overcommitted the host by allocating too much RAM to the VMs (keeping in mind that ESXi itself will want ~2 GBytes of your 8 GByte host RAM).  The latter situation can also be somewhat mitigated by ensuring that your VMs have VMware Tools (and particularly the balloon driver) loaded.

I agree that the overcommitment of processor cores should not cause any further degradation after a period of time that would not already be evident if the same workload were run as soon as the VM was powered on.  That said, efficiently running 2 VMs with two cores apiece on a host with two cores (even four hyperthreaded cores) is going to require great care.

Good luck...

--

Darius

[MacSS]

I have 8GB of ram in the system running 2 OSX 10.9 VMs both allocated 4GB of ram.

Are you saying that if I have 8GB of ram that I should only give the VMs 6GB?

Also, do you have link for how to install the VM tools? I have never done that on my VMs.

Thanks for for your help!

John

[thorsfall]

I'm running a Mac Mini 6,2 with the Core i7 processor and 16GB RAM, and I see behaviour similar to what you're describing here, especially if the VM is being run from the internal HDD (i.e. the POS that Apple shipped in the box).  I routinely see OSX guest VMs slow down to a crawl or jam up entirely, and often require a reset of the VM in order to recover.  As soon as the VM is rebooted, it runs relatively quickly again for a period before slowing down all over again.  I put a lot of this behaviour down to disk latency.  OSX appears to be a terrible guest, always thrashing around on disk and doing something akin to a defrag, which causes thin provisioned volumes to expand to 100% of their allocated size within a week or so.  I installed a dual-disk kit and a Samsung Pro 256GB SSD to run two of my important VMs, and now these two VMs are seemingly never affected by the "slow down".

Other VMs running on the Apple-supplied 2.5" 5400RPM HDD routinely stall, jam up and otherwise exhibit infuriating delays, but I find that this can be reconciled with the I/O latency being displayed in the vSphere Client's performance graphs.  When disk latency jumps over 100ms, I experience these "slow downs".  It's probably well worth checking to see if this is happening on your Mac Mini.  If not, then at least you've excluded it as a cause.

[MacSS]

OK,

So I installed the VM tools for both VMS. Can you tell me what the balloon driver is, and what I need to do to install or modify it?

Also, I found a setting for the swap file in the VMs and if the file should be stored on Automatically, in the same folder as the VM, or in the datastore of the VMs. Do you think changing this from automatic may help?

Gian

[hapip87]

Hi

Regarding the Ballon driver its already installed along with vm tools

ballooning is a memory reclamation  technique used when and ESXi host is running low on memory

swapping

When you setup a VM, you allocate resources for that VM based on usage, user access, and so on. Once you assign resources to a VM, the VM is no longer aware of how much resources are consumed by other VMs in a host. For example, when you have three VMs in a host and two of them are consuming the assigned memory, the third VM will have performance issues. This usually leads to various bottlenecks and you’ll very often find yourself in such situations which leaves you scrambling – troubleshooting to ensure VM performance or availability issues don’t affect end users.