I'll summarize my Understanding VMware series for you today.
VMware provide Ready Time as a number of seconds
in an interval. It’s possible to convert this using the interval length into a
% value. Anything more than 10% Ready Time is likely to indicate unacceptable
performance.
Ready time is important. It’s
a measure that directly shows negative effects on service time.
Any
ready time accumulated has an impact on performance. (Although it may still be
acceptable performance)
It’s
not enough to monitor CPU%, you need to monitor Ready Time as well. The more
vCPUs a VM has, the harder it is to schedule it onto the CPU threads available.
Use as few vCPUs as possible.
Memory is not just about
occupancy. Make sure you look at ballooning, active and swap as well.
- Ballooned Memory works by “robbing Peter to pay Paul”.
- Active Memory is the amount of memory the VM has accessed in the last 20 seconds.
- Swap takes place in the cases where ballooning and page sharing are not sufficient to reclaim memory, ESX employs hypervisor swapping to reclaim memory.
Disk latency can be
observed and broken down to internal and external to VMware. There are
3 metrics: Queue Latency Kernel Latency Device Latency. We only get Queue if we’re not getting
the performance we require out of Kernel
and Device. So Kernel
and Device remain
the focus of any investigation into poor IO performance.
VMware Cluster Planning. To report
back on the number of VMs you can fit in a cluster,
decide what the size of your cluster actually is for this exercise.
Find a good peak to work with and trend your results
over time. It’s not a static
picture.
If you've enjoyed my series then go to our Resources section where you can watch webinars on-demand and download VMware capacity management white papers and more.
Phil Bell
Consultant
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