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

For supported multipathing configurations, see the HP Integrity Virtual Machines 4.2: Release
Notes.
7.2.1.4 VM Storage Management
Before you decide how to divide VM Host storage, consider the impact on the management of
the storage subsystem.
A VM Host administrator manages VM storage to make sure virtual media is allocated safely.
This begins with understanding the VM Host I/O stack and knowing from where the virtual
media is being allocated.
Figure 7-3 shows an example of a VM Host I/O stack as it applies to a single LUN.
Figure 7-3 Sub-LUN Storage Allocation Example
File File File File File File File File
2 2
Logical Volume Logical Volume Logical Volume Logical Volume
Whole Disk
1
2
The virtual machine is allocated a logical volume from the LUN for a Virtual LvDisk.
• The logical volume that has been allocated is labeled 1.
• The parts of the disk that cannot be allocated are labeled 2.
Those parts that are no longer available include the files that were on the logical volume and the
whole disk that makes up part of the volume group. If any of these parts are allocated for other
virtual devices, data corruption can occur on the Virtual LvDisk.
Those parts that are still available for reallocation include other logical volumes that are on the
disk,and files that are on those other logical volumes on the disk. These pieces can be allocated
without data corruption problems because they do not overlap with the Virtual LvDisk.
Beyond avoiding sub-LUN collisions, whole LUN collisions also need to be avoided. The same
storage resource, virtual or attached, cannot be specified more than once to the same virtual
machine. HP-UX 11i v3 supports both legacy per-path device files (for example, /dev/rdsk/
c6t2d0) and agile non-path specific device files (for example, /dev/rdisk/disk16). As shown
in Figure 7-4, there may be more than one legacy device file that points to the same physical
storage device, while there is only one agile device file per a given physical storage device. Use
of agile device files is recommended to avoid whole LUN collisions.
Figure 7-4 Bad Multipath Virtual Media Allocation
Physical
Adapter
Physical
Adapter
Physical
Storage
/dev/rdsk/c6t2d1 /dev/rdsk/c11t2d1
Also, the same storage resource, virtual or attached, cannot be simultaneously shared between
virtual machines, unless otherwise specifically exempted. Figure 7-5 shows a Virtual LvDisk
being shared across virtual machines, which is not supported.
106 Creating Virtual Storage Devices