HP Integrity Virtual Machines 4.2: Installation, Configuration, and Administration
Figure 7-1 Integrity VM Storage I/O Stack
HP-UX
Interface Driver
HP-UX
Interface Driver
HP-UX
Interface Driver
Physical Adapter Physical Adapter Physical Adapter
Physical Media Physical Media Physical Media
VM Host Driver Services
File Systems Layer
Virtual File Disk
Logical Volume Managers Layer
Virtual LvDisk
Disk Drivers Layer
Virtual Disk
Attached Devices
Integrity Vm Passthrough
Drivers Layer
For a virtual I/O operation to be completed, it has to travel round trip between the virtual storage
adapter and the VM Host physical storage device. The longer the path is, the longer it takes for
virtual I/O to be completed. As shown in Figure 7-1, a virtual I/O operation must traverse each
software layer in order, from where it originates to the physical media. For example, a virtual
I/O operation for a Virtual FileDisk must traverse any logical volume managers the file system
is on and the disk drivers that control the whole disk. Therefore, in general, the higher the virtual
media is in the VM Host I/O stack, the slower it operates.
The simplified I/O stack in Figure 7-1 does not completely illustrate all the choices that can affect
the performance:
• 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, a file system's buffer cache may help a Virtual FileDisk perform better on some
I/O workloads than the other virtual device types, which have no such caching.
For further information on tuning performance at each software layer on the VM Host, see the
Integrity VM white papers on the HP Documentation website at http://docs.hp.com.
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 somewhere in the data center. You can
help ensure the best performance by understanding the impact of the physical storage and the
way I/O accesses it.
104 Creating Virtual Storage Devices