Chapter 3. Virtualization 143
Virtual SCSI
Virtual SCSI is used to refer to a virtualized implementation of the SCSI protocol. Virtual SCSI
is based on a client/server relationship. The Virtual I/O Server logical partition owns the
physical resources and acts as a server or, in SCSI terms, a target device. The client logical
partitions access the virtual SCSI backing storage devices provided by the Virtual I/O Server
as clients.
The virtual I/O adapters (virtual SCSI server adapter and a virtual SCSI client adapter) are
configured using a managed console or through the Integrated Virtualization Manager on
smaller systems. The virtual SCSI server (target) adapter is responsible for executing any
SCSI commands that it receives. It is owned by the Virtual I/O Server partition. The virtual
SCSI client adapter allows a client partition to access physical SCSI and SAN attached
devices and LUNs that are assigned to the client partition. The provisioning of virtual disk
resources is provided by the Virtual I/O Server.
Physical disks presented to the Virtual/O Server can be exported and assigned to a client
partition in a number of ways:
The entire disk is presented to the client partition.
The disk is divided into several logical volumes, which can be presented to a single client
or multiple clients.
As of Virtual I/O Server 1.5, files can be created on these disks, and file-backed storage
devices can be created.
The logical volumes or files can be assigned to separate partitions. Therefore, virtual SCSI
enables sharing of adapters and disk devices.
Figure 3-12 shows an example where one physical disk is divided into two logical volumes by
the Virtual I/O Server. Each client partition is assigned one logical volume, which is then
accessed through a virtual I/O adapter (VSCSI Client Adapter). Inside the partition, the disk is
seen as a normal
hdisk.
Figure 3-12 Architectural view of virtual SCSI
Client Partition 1 Client Partition 2I/O Server Partition
POWER Hypervisor
LVM
Physical
Adapter
Hdisk Hdisk
Logical
Volume 1
Logical
Volume 2
VSCSI
Server
Adapter
VSCSI
Client
Adapter
VSCSI
Client
Adapter
Physical Disk
(SCSI, FC)
VSCSI
Server
Adapter
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