HP Integrity Virtual Machines Installation, Configuration, and Administration Version A.03.50

Figure 7-5 Bad Virtual Device Allocation
Guest A Guest B
Virtual
LvDisk
As these examples illustrate, it is important to know where storage is allocated from to avoid
data corruption with virtual machines or even the VM Host. Management utilities such as HP
System Administration Manager (sam) and the System Management Homepage (SMH) utilities
allow you to track disk devices, volume groups, logical volumes, and file systems. You can use
these utilities to annotate devices so that VM Host administrators can see exactly which virtual
machines are using each VM Host storage device.
To show each disk only once, management utilities consolidate multipath devices into one disk.
When you are dividing up the disk, you should use all the parts of a single disk on a single virtual
machine. Allocating different parts of the same disk to different virtual machines makes it difficult
to manage and to isolate problems.
7.2.1.5 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 to change virtual media depends on the type of virtual media used. Whole disks are
not normally adjustable in terms of size, but some high-end storage enclosures might permit the
adjustment of a LUN without losing that LUN's data. Logical volumes are adjustable without
losing any data. Finally, files can be changed easily with VM Host file system commands.
No changes to any virtual media can take place on the VM Host until the virtual device that uses
the 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.
This coordination might also be necessary for attached I/O devices. Once a VM Host device is
attached to the virtual machine, it is controlled and owned by that virtual machine. Modifications
to the attached device, like changing a tape, can be done physically without detaching the device
from the guest. However, such changes might need to be coordinated with the VM Host
administrator, especially if the guest administrator has no physical access to the device attached
to the virtual machine.
All types of virtual storage devices can be added and removed dynamically from virtual machines.
That is, virtual disks, virtual DVDs, tapes, media changers, and CD/DVD burners are all
hot-swappable. However, the virtual storage adapters are currently not hot-swappable. Therefore,
if all the virtual storage adapters are full, you must reboot the virtual machine when you add
additional devices.
7.2.1.6 Virtual Storage Setup Time
Some virtual devices take longer to set up than others. Whole disks are very easy to set up because
they require nothing more than a character device file. This is usually created automatically
when the VM Host system is booted.
90 Creating Virtual Storage Devices