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to the same physical disk. Once the /dev/rdsk/c6t2d0 device file is specified for a Virtual Disk, the
/dev/rdsk/c11t2d0 device file is no longer available.
Figure 6-4 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 6-5 shows a Virtual LvDisk being shared across
virtual machines, which is not supported.
Figure 6-5 Bad Virtual Device Allocation
Guest A Guest B
Virtual
LvDisk
As theseexamples illustrate, it isimportant to know wherestorage is allocated fromto avoiddata corruption
with virtual machines or even the VM Host. Use the HP System Administration Manager or the sam(1M)
utility. The sam utility provides the ability to track disk devices, volume groups, logical volumes, and file
systems. It attempts to consolidate multipaths to not show disks more than once. Additionally, it provides
the ability to annotate devices so that VM Host administrators can see exactly which virtual machines are
using what VM Host storage devices. The sam utility does not track individual disk partitions. However,
you should use all of the parts of a single disk on a single virtual machine when you are dividing up the
disk. Allocating different parts of the same disk to different virtual machines makes it difficult to manage
and to isolate problems.
6.2.1.5 VM Storage Changes
Depending on how you set up storage for a virtual machine, the resulting configuration can be more or
less difficult to change.
The ability tochange virtual mediadepends on the typeof virtual media used.Whole disks are notnormally
adjustable in terms of size, but some high-end storage enclosures may permit the adjustment of a LUN
without losing thatLUN's data. Disk partitions arenot adjustable without losing thedisk's data. However,
soft partitions, such as logicalvolumes, are adjustable withoutlosing any data. Finally, files can be changed
easily with VM Host file system commands.
No changes toany virtual media cantake place on theVM Host until thevirtual device that usesthe media
is removed from the active VM. Attempts to change virtual devices that have I/O active on them is denied
by the hpvmmodify command. Once an active virtual machine is allocated virtual media for a virtual
device, that virtual machine owns that media and can access it any time. VM Host administrators need to
coordinate with VM guest administrators about active virtual machine changes, if the two roles are served
by different individuals.
68 Creating Virtual Storage Devices