IBM Power 570 Technical Overview And Introduction page 98

4405ch03 Virtualization.fm
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 server or, in SCSI terms, 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 an HMC or through the Integrated Virtualization Manager on smaller
systems. The virtual SCSI server (target) adapter is responsible for executing any SCSI
commands 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 different ways:
The entire disk is presented to the client partition
The disk is divided into several logical volumes, these can be presented to a single client
or multiple different 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 different partitions. Therefore, virtual SCSI
enables sharing of adapters as well as disk devices.
Figure 3-4 shows an example where one physical disk is divided into two logical volumes by
the Virtual I/O Server. Each of the two client partitions 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 3-4 Architectural view of virtual SCSI
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IBM Power 570 Technical Overview and Introduction
Draft Document for Review September 2, 2008 5:05 pm