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

7.1.1.4 Storage Security
To avoid problems while supporting multiple virtual machines on one physical machine, Integrity
VM isolates each virtual machine. Using Integrity VM commands, the VM Host administrator
determines the physical storage resources that each virtual machine can access. This storage
isolation is maintained by the Integrity VM storage subsystem through DMA boundary checks
on each virtual machine I/O operation, thereby insuring that one virtual machine does not access
the memory of another.
7.1.1.5 Storage Configurability
VM Host administrators expect the virtual machines to be as easily configurable as HP Integrity
servers. The Integrity VM storage subsystem allows for easy changes of the storage devices
through Integrity VM commands. Using these commands, the VM Host administrator dynamically
adds, deletes, and modifies storage devices on virtual machines. Guest administrators can change
some storage, limited in scope by the VM Host administrator, using the virtual console.
7.1.2 Integrity VM Storage Architectures
To provide the flexibility required to meet a variety of data center needs, the Integrity VM storage
subsystem consists of two storage architectures: Section 7.1.2.1 (page 82) and Section 7.1.2.2
(page 83).
7.1.2.1 Shared I/O
The shared I/O architecture is a means by which a virtual machine accesses an entirely virtualized
storage subsystem provided by Integrity VM. The Integrity VM storage subsystem emulates real
hardware to the virtual machine while interacting with the VM Host to complete the virtual
machine I/O operation to the VM Host storage entity. This abstraction provides the ability of a
VM Host administrator to share physical VM Host storage hardware across multiple virtual
machines and to allocate that storage at sub-LUN levels.
The sharing of individual storage LUNs is accomplished by dividing a VM Host LUN into smaller
parts, like logical volumes, or files. Each of these sub-LUN VM Host entities can then be used as
media for separate virtual storage devices. Virtual machines access the virtual storage devices
as real storage devices, with no knowledge that the virtual storage media is actually a sub-LUN
VM Host entity.
The way the virtual storage media is accessed by the Integrity VM storage subsystem allows
virtual machines to share physical VM Host storage adapters. All virtual storage media is accessed
through user-defined interfaces on the VM Host. The VM Host maintains complete control of
the physical hardware and handles the virtual machine I/O operations just as it would be handled
for any other user application. Thus, just as hardware is shared among normal applications
running on the VM Host, virtual machine I/O is shared across the physical storage as well.
This architecture also provides for whole LUNs to be virtualized. While this does not increase
storage utilization, it does provide higher storage availability. Because the LUN is virtualized,
the guest OS does not have to support the physical VM Host LUN. It only has to be able to
support the virtualized version of it. Thus by using shared I/O, a virtual machine can run with
any physical hardware that is supported by the VM Host.
Finally, all virtual machine I/O requests in shared IO are processed by virtual adapters. A virtual
adapter is either an emulation of a real adapter that a native guest OS driver accesses as real
hardware, or a special driver loaded into the guest OS. In either case, the virtual adapter uses
internal Integrity VM storage subsystem calls to handle communication of virtual machine I/O
to the virtual devices. This connection between the virtual adapter and the virtual devices need
not resemble anything in an HP Integrity server system. It is emulated so that the virtual machine
does not know the difference.
82 Creating Virtual Storage Devices