HP-UX vPars and Integrity VM V6.3 Administrator Guide

• Performance of different software layers differs.
• The interfaces to each software layer are different, allowing Integrity VM different ways to
send I/O through the layers.
For example, whole disks can achieve higher throughput rates than logical volumes and file
systems.
• The I/O layer might have features to help performance increase beyond a lower layer.
For example, the file cache of the file system might help a Virtual FileDisk perform better on
some I/O workloads than the other virtual device types, which have no such caching.
For more information about tuning performance at each software layer on the VSP, see the vPars
and Integrity VM white papers at http://www.hp.com/go/hpux-hpvm-docs.
When you configure virtual devices, consider how the virtual media maps to the physical storage.
All virtual media connects to a piece of physical media in the data center. You can ensure the best
performance by understanding the impact of the physical storage and the way I/O accesses it.
It is important to know where the virtual media is located on physical storage devices. With vPars
and Integrity VM, a single physical disk might be sliced into logical volumes or files. Slicing up
physical disks increases utilization, but it can affect the performance of the physical device. The
guest OS treats the virtual disk as a whole disk, not as a part of a physical one. Over-slicing
physical storage can overload the ability of a physical device to handle virtual I/O that is meant
for whole disks. Figure 7 (page 68) shows a common mistake of overdriving physical storage with
multiple guest OS boot disks, which are often I/O intensive.
Figure 7 Overdriving physical storage hurts performance
Virtualization Services Platform (VSP)
Guest Boot Disk Guest Boot Disk Guest Boot Disk
Overdriven Physical Storage
Guest 1 Guest 2 Guest 3
You can provide workloads that the physical devices can handle for all the virtual devices layered
on top of them. You can use the performance tools on the VSP, such as sar(1M), to see how the
physical storage is keeping up with the virtual device demands.
68 Storage devices