HP Integrity Virtual Machines 4.3: Installation, Configuration, Administration

6.1.2.2 Attached I/O
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.
6.1.3 Attached Device Support in AVIO
AVIO storage supports attached devices (tapes, changers and burners) on HP-UX 11i v2 and
HP-UX 11i v3 guests. Attached devices configured using AVIO (avio_stor adapter), have the
following benefit over attached devices configured with VIO (scsi adapter):
• Allow sharing of tapes, changers, and burners among multiple guests and host
• Support of USB 2.0 DVD burners
• Improved performance
The resource specifier for attached devices using AVIO (avio_stor adapter) is different from
the VIO (scsi adapter) resource specifier. See Section 6.1.3.1 (page 85) for the new syntax.
With VIO (scsi adapter type), USB CD/DVD devices are not supported for use as attachable
media. AVIO (avio_stor adapter type) supports USB 2.0 DVD burners.
To identify USB CD/DVD devices, use the ioscan -fun command.
NOTE: Because Integrity VM may do four to six calls to open() on a DVD when accessing it,
and hpvmcreate or hpvmmodify command might take more than a minute to complete when
there is no media in the drive. Example commands that could appear to hang are:
# hpvmcreate -P guest -a dvd:scsi::disk:/dev/rdisk/disk5
# hpvmcreate -P guest -a dvd:scsi::null:/dev/rdisk/disk5
# hpvmmodify -P guest -a dvd:scsi::disk:/dev/rdisk/disk5
# hpvmmodify -P guest -a dvd:scsi::null:/dev/rdisk/disk5
6.1.3.1 Resource Syntax
AVIO storage requires the hardware path of the lunpath class (displayed only in ioscan with the
-N option) to be specified in place of device special files in a resource specifier. Here is the syntax
of the resource specifier:
6.1 Introduction to Integrity VM Storage 85