HP Capacity Advisor 7.2 User Guide

• Capacity Advisor usually reports CPU utilization that is greater than what is reported by the
VM guest. The operating system inside a virtual machine only knows about the CPU time used
by threads that simulate the virtual processors. However, there are also threads that simulate
the I/O cards and disks in the virtual system. Capacity Advisor collects data on all of these
threads, which can cause the Capacity Advisor data for a specific virtual machine’s CPU
utilization to be greater than the number of virtual CPU cores (vCPUs) associated with the
virtual machine. Under certain load conditions, this can result in CPU utilization of more than
100% being reported for a virtual machine.
• Capacity Advisor data for VM host CPU utilization can be lower than what the guest operating
system reports, especially during periods of high utilization. Capacity Advisor records physical
CPU utilization, which is the utilization of the actual cores on the VM host; that is, the total
utilization reported by Capacity Advisor is based on the CPU time that the VM host allotted
to each virtual machine. In contrast, the guest OS records virtual CPU utilization, which includes
time when the VM wants to run, but is suspended while another VM is using the resources on
the VM host.
Because Capacity Advisor corrects for these effects, the collected data has much less “noise” in
it, and better reflects the CPU time that was actually used by any one VM.
Data normalization
Capacity Advisor makes certain assumptions in its data analysis. These assumptions include
automatically adjusting for CPU platform differences based on a performance index. (The
performance index is constructed by normalizing collected data to selected benchmarks for the
source and destination systems).
If desired, you can add your own benchmark values to the database for use in calculating the
performance index for workload moves among systems with the same or different architectures.
(See capcustombenchmark in the Appendix (page 193) for more information.
Memory, network IO, and disk IO usage are not normalized.
Resources for which Capacity Advisor collects data
Capacity Advisor collects data for utilization of the following resources:
• CPU cores
• Memory
• Network I/O
• Disk I/O
• Power
Upper bounds
Upper bounds represent the maximum capacity of a resource for a given system. The maximum
capacity is used in Capacity Advisor for items such as the network and disk I/O utilization graphs
of systems, the graphs and values shown in a profile viewer, and the HP Smart Solver calculations.
CPU capacity
The maximum CPU capacity of a system is the product of the number of CPU cores and the clock
speed of the system.
Memory
The maximum capacity of memory is the amount of memory on the system.
Network I/O
The maximum capacity for network I/O defaults to the high-water mark (that is, the maximum
observed or collected value) for network I/O. However, to set the upper bound to a value you
24 Key Capacity Advisor concepts