As I mentioned on Friday the large
difference between what the OS thinks is happening and what is really happening
all comes down to time slicing.
In a typical VMware host we have
more vCPUs assigned to VMs than we do physical cores.
The processing time of the cores
has to be shared among the vCPUs. Cores are shared between vCPUs in time slices,
1 vCPU to 1 core at any point in time.
More vCPUs lead to more time
slicing. The more vCPUs we have the less time each can be on the core, and
therefore the slower time passes for that VM.
To keep the VM in time extra time interrupts are sent in quick
succession. So time passes slowly and
then very fast.
More time slicing equals less
accurate data from the OS.
Anything that doesn’t relate to time, such as disc
occupancy should be ok to use.
On Wednesday I'll be dealing with Ready Time, you've still got time to register to come along to my webinar 'VMware and Hyper-V Virtualization over-subscription(What's so scary?) taking place on October 12. http://www.metron-athene.com/services/webinars/index.html
Phil Bell
Consultant
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