Introduction to Integrity VM Storage

The main purpose of Integrity VM is to increase system resource utilization on Integrity servers. The Integrity VM storage subsystem meets this goal by permitting multiple virtual machines to share a variety of physical storage adapters and devices that are available on an Integrity server. Furthermore, the Integrity VM storage subsystem allows for a single storage LUN on the VM Host to be carved up into smaller entities that can be used as separate individual disks or DVDs on the virtual platform.

Like HP Integrity servers, it is expected that virtual machines will have several different storage device types available for use. The Integrity VM storage subsystem provides for disks, DVDs, tapes and media changers to be used by a guest OS. Additionally, the way that virtualization abstracts the physical hardware provides a common supportable interface for a guest OS to interact with. Because a guest OS only accesses Integrity VM virtual hardware, the guest OS can use physical hardware that it does not support on an Integrity server.

Each release of the Integrity VM storage subsystem strives to improve performance. Performance is improved in each release by lowering costs of virtualization, exploiting new features in the VM Host, and tuning operating systems for the virtual platform. At the same time, Integrity VM provides more virtualization choices to VM Host administrators, so that they can find the best balance between virtualization and performance to meet their needs.

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 ensuring that one virtual machine does not access the memory of another.

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.

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 I/O 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.

Attached I/O allows a virtual machine to access to a VM Host LUN directly. In this architecture, the Integrity VM storage subsystem attaches a LUN on the VM Host to a virtualized storage adapter. A LUN can be a disk, DVD, tape, media changer, or other peripheral device types. Because attached I/O does not require device virtualization, the performance of attached I/O might be better than shared I/O.

The main difference between shared I/O and attached I/O is the degree to which a physical storage subsystem is virtualized. In shared I/O, an entire storage subsystem is virtualized. Therefore, all physical adapters on the VM Host and all the storage connected to those adapters may be shared among virtual machines. In attached I/O, only the storage adapter is virtualized. Therefore, only the VM Host physical storage adapters may be shared. At least one LUN, the attached LUN, cannot be shared. It is owned and solely controlled by the virtual machine it is attached to.

To provide the VM with complete control over attached devices, the Integrity VM storage subsystem interprets I/O requests from the guest device drivers into I/O requests that can be completed by the VM Host storage subsystem on the guest's behalf. In the process, the VM Host storage subsystem sends all the actual data and responses back the guest device drivers. With all this data, the guest device driver is in complete control over the device. As such, the guest OS must have built-in support for the attached VM Host LUN to use it.

Attached I/O uses a virtual adapter to communicate with the guest OS and the attached LUN. The virtual adapter either can be an emulation of a real adapter or it can be controlled by a special driver loaded into the guest OS. Either solution produces a virtual adapter that communicates with both virtual devices and attached physical devices.

Integrity VM provides two types of virtual PCI storage adapters to process virtual storage I/O requests:

All supported guest operating systems contain native MPT SCSI adapter drivers that communicate with this PCI register emulation. All virtual and attachable devices can be used with this single virtual storage adapter.

The AVIO storage adapter is a high performance adapter and needs guest OS drivers. AVIO supports up to 128 storage devices per guest aqnd also leverages the VM Host 11i v3 storage stack features to provide better storage manageability in the guest. AVIO is currently supported on both HP-UX 11i v2 and 11i v3 guests, for disks and DVD guest devices, and for host disk, file and LVM (non-VmVM) backing stores. HP recommends the use of AVIO for HP-UX 11i v2 and 11i v3 guests for the supported guest devices and host backing stores.

Integrity VM supports a variety of virtual and attachable devices. Disk and DVD-ROM devices support several virtual media types (see Section ). Physical tapes, media changers, and CD/DVD burners are attachable; they can be used to perform data backups directly from a virtual machine (see Section ).

Attached Devices

Integrity VM supports a suite of attached devices to complete data backups from a virtual machine. Integrity VM attaches these devices using a special Integrity VM pass-through driver. With this pass-through driver, virtual machine I/O requests are interpreted by Integrity VM and sent through the virtual storage subsystem to the physical device. The virtual storage subsystem sends device responses to the Integrity VM pass-through driver, which sends the responses to the virtual machine. Because the virtual machine can see all the data and responses, support for the attached physical device must be provided by the guest OS. An attached device can be attached to only one virtual machine at a time.

Attached devices include:

• CD/DVD burners

• Media changers

• Tape devices

The maximum transfer size can be 1 MB for any guest operating system.

	NOTE: Only HP-UX guests can use AVIO, and the backing store can be only file, disk or volume. There is no attached AVIO device support, and guest devices can be only disk or DVD.