HP Integrity Virtual Machines 4.2: Installation, Configuration, and Administration

It is important to know exactly where the virtual media is located on physical storage devices.
With 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 a physical device's ability to handle virtual I/O that is meant for
whole disks. Figure 7-2 shows a common mistake of overdriving physical storage with multiple
guest OS boot disks, which are often I/O intensive.
Figure 7-2 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 VM Host, 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 7-1, all virtual I/O goes through a general VM Host I/O services
layer that routes the virtual I/O to the correct VM Host 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 VM Host. For help with selecting a multipath solution for a virtual
media type, see Section 7.2.1.3 (page 105).
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.
7.2.1.3 VM Storage Multipath Solutions
Integrity VM virtual devices support the built-in multipathing of the HP-UX 11i v3 VM Host,
which is enabled by default to provide improved performance, load-balancing, and higher
availability for 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 VM Host for the following reasons:
• The VM Host 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 virtual
machine I/O with which it is competing on the VM Host (see Figure 7-1).
• Running a multipath solution in a virtual machine 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 VM Host.
Errors in communication to the virtual media are properly emulated as media errors sent
to the guest OS, not as path failures.
• The VM Host does not return specific errors to Integrity VM for hardware path failures.
Integrity VM does not detect such events and does not pass them to the virtual machine.
7.2 Configuring Integrity VM Storage 105