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Chapter 2. Architecture and technical overview 49
2.11.1 POWER Hypervisor
Combined with features designed into the POWER5 and POWER5+ processors, the POWER
Hypervisor delivers functions that enable other system technologies, including
Micro-Partitioning technology, virtualized processors, IEEE VLAN, compatible virtual switch,
virtual SCSI adapters, and virtual consoles. The POWER Hypervisor is a basic component of
system firmware that is always active, regardless of the system configuration.
The POWER Hypervisor provides the following functions:
Provides an abstraction between the physical hardware resources and the logical
partitions using them.
Enforces partition integrity by providing a security layer between logical partitions.
Controls the dispatch of virtual processors to physical processors. (For more information,
see 2.12.2, “Logical, virtual, and physical processor mapping” on page 52.)
Saves and restores all processor state information during logical processor context switch.
Controls hardware I/O interrupt management facilities for logical partitions.
Provides virtual LAN channels between physical partitions that help to reduce the need for
physical Ethernet adapters for inter-partition communication.
The POWER Hypervisor is always active when the server is running, whether the server is
partitioned or not, and also even when the server is not connected to the HMC. It requires
memory to support the logical partitions on the server. The amount of memory required by the
POWER Hypervisor firmware varies according to several factors. Factors influencing the
POWER Hypervisor memory requirements include the following:
Number of logical partitions
Partition environments of the logical partitions
Number of physical and virtual I/O devices used by the logical partitions
Maximum memory values given to the logical partitions
The minimum amount of physical memory for each partition is 128 MB, but in most cases the
actual requirements and recommendations are between 256 MB and 512 MB for AIX 5L,
Red Hat Linux, and Novell SUSE Linux. Physical memory is assigned to partitions in
increments of Logical Memory Block (LMB). For POWER5+ processor-based systems, LMB
can be adjusted from 16 MB to 256 MB.
The POWER Hypervisor provides the following types of virtual I/O adapters:
Virtual SCSI
Virtual Ethernet
Virtual (TTY) console
Virtual SCSI
The POWER Hypervisor provides a virtual SCSI mechanism for virtualization of storage
devices (a special logical partition to install the Virtual I/O Server is required to use this
feature, see 2.12.3, “Virtual I/O Server” on page 54). The storage virtualization is
accomplished using two paired adapters: a virtual SCSI server adapter and a virtual SCSI
Note: Use the System Planning Tool to estimate the memory requirements of the POWER
Hypervisor.
In AIX 5L V5.3, the lparstat command using the -h and -H flags displays the POWER
Hypervisor statistical data. Using the -h flag adds summary POWER Hypervisor statistics
to the default lparstat output.