HP vPars and Integrity Virtual Machines V6.1 Administrator Guide

help ensure the best performance by understanding the impact of the physical storage and the
way I/O accesses it.
It is important to know exactly where the virtual media is located on physical storage devices. With
vPars and Integrity VM V6.1, 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 a physical device's ability to handle virtual I/O that is
meant for whole disks. Figure 6 shows a common mistake of overdriving physical storage with
multiple guest OS boot disks, which are often I/O intensive.
Figure 6 Overdriving Physical Storage Hurts Performance
Guest
Boot Disk
Guest
Boot Disk
Overdriven
Physical Storage
Guest
Boot Disk
Provide workloads that the physical devices can handle for all the virtual devices layered on top
of them. Use performance tools on the VSP, like sar(1M), to see how the physical storage is keeping
up with the virtual device demands.
The way the virtual media I/O gets to the physical storage backing it is also an important
consideration. As shown in Figure 5, all virtual I/O goes through a general VSP I/O services layer
that routes the virtual I/O to the correct VSP interface driver. The interface driver then controls the
physical I/O adapter to issue virtual I/O to the physical storage device. By load balancing across
these physical adapters, virtual I/O bottlenecks can be eliminated at the physical hardware layers,
thereby increasing performance. Load balancing can be done by using a multipathing solution on
the VSP. For help with selecting a multipath solution for a virtual media type, see Section 9.2.1.3
(page 118).
The performance of attached devices is largely determined by the type of physical device attached
to the virtual machine. Tapes, media changers, and CD/DVD burners are inherently slow devices,
not significantly impacted by the software overhead of Integrity VM.
9.2.1.3 Storage multipath solutions
vPars and Integrity VM virtual devices support the built-in multipathing of the HP-UX 11i v3 VSP,
which is enabled by default to provide improved performance, load-balancing, and higher
availability for vPars/VMs. Currently, there are no multipath solutions supported for the attachable
device types of tapes, media changers, and CD/DVD burners.
There are no multiple paths inside a virtual machine to virtual devices. Multipathing is supported
only on the VSP for the following reasons:
• The VSP is the only place where all virtual I/O can be properly load balanced for the best
overall performance. A single virtual machine cannot account for all the other vPar/VM I/O
with which it is competing on the VSP (see Figure 5).
• Running a multipath solution in a vPar/VM does not provide any high availability for a virtual
device. Virtual connections between virtual adapters and their devices are never lost until an
hpvmmodify command is used to disconnect them. The only connection ever lost is the ability
of a virtual device to access its own virtual media through the VSP. Errors in communication
118 Creating virtual storage devices