Partition resources
Logical partitioning allows you to assign dedicated processors or, when you use the Micro-Partitioning™ feature of POWER5- and POWER6-based systems, to assign processing units to partitions. You can define a partition with a processor capacity as small as 0.10 processing units, which represents 10% of a physical processor. You can also assign physical memory and physical I/O devices or virtual I/O-devices (SCSI or Ethernet) to partitions.
Partition and system profiles
The information about resources that are assigned to a partition is stored in a partition profile. Each partition can have multiple partition profiles. By switching from one partition profile to another, you can change how resources are assigned.
To change partition profiles, shut down the operating system instance that is running in the partition and stop (deactivate) the partition. There are two types of profiles, partition and system, as explained here:
Partition profile A partition profile stores the information about the assigned resources for a specific partition, such as processor, memory, physical I/O devices, and virtual I/O devices (Ethernet, serial, and SCSI). Each partition must have a unique name and at least one partition profile. A partition can have several partition profiles, but it reads only one partition profile when it is started (activated).
You select a partition profile when you activate the partition. Otherwise, the default partition profile is used. You can designate any partition profile as the default partition profile. If there is only one partition profile for a partition, it is always the default.
System profile A system profile provides a collection of partition profiles that should be started at the same time. The partition profiles are activated in the order of the list that is defined in the system profile.
Processors
Partitions can have processors dedicated to them, or they can have their processors virtualized from a pool of shared physical processors This is known as Micro-Partitioning technology. With this technology, both types of partitions can coexist in the same system at the same time.
Micro-Partitioning technology differs from dedicated processor partitions in that physical processors are abstracted into virtual processors, which are then assigned to partitions. These virtual processors have capacities ranging from 10% of a physical processor up to the entire processor. Therefore, a system can have multiple partitions that share the same physical processor, and that divide the processing capacity among themselves.
A dedicated processor partition, such as the partitions that are used on POWER4™ processor-based servers, have an entire processor that is assigned to a partition. These processors are owned by the partition where they are running and are not shared with other partitions. Also, the amount of processing capacity on the partition is limited by the total processing capacity of the number of processors configured in that partition, and it cannot go over this capacity (unless you add or move more processors from another partition to the partition that is using a dynamic LPAR operation).
Memory
To support any operating system (including AIX and Linux) which requires real mode code execution and the ability to present a real address space starting at zero (0) to each partition in the system, the logical memory concept is adopted.
Logical memory is an abstract representation that provides a contiguous memory address to a partition. Multiple non-contiguous physical memory blocks are mapped to provide a contiguous logical memory address space.
The logical address space provides the isolation and security of the partition operating system from direct access to physical memory, allowing the hypervisor to police valid logical address ranges assigned to the partition. The contiguous nature of the logical address space is used more for simplifying the hypervisor's per-partition policing than it is used because it is an operating system requirement. The operating system's VMM handles the logical memory as though it were physical memory in a non-partitioned environment.
In a partitioned environment, some of the physical memory areas are reserved by several system functions to enable partitioning in the partitioning-capable pSeries server. You can assign unused physical memory to a partition. You do not have to specify the precise address of the assigned physical memory in the partition profile, because the system selects the resources automatically.
Depending on the overall memory in your system and the maximum memory values that you choose for each partition, the server firmware must have enough memory to perform logical partition tasks. Each partition has a Hardware Page Table (HPT). The size of the HPT is based on an HPT ratio of 1/64 and is determined by the maximum memory values that you establish for each partition.
Physical I/O slots
Physical I/O devices are assignable to partitions on a PCI slot (physical PCI connector) basis. It is not the PCI adapters in the PCI slots that are assigned as partition resources, but the PCI slots into which the PCI adapters are plugged.
When using physical I/O devices to install an operating system, you have to assign at least one, typically an SCSI adapter that is able to boot the operating system, and an adapter to access the install media. Instead of physical I/O devices, you can assign a virtual I/O device that behaves like a physical I/O device.
After installation, you need at least one physical device adapter that is connected to the boot disk or disks. For application use and system management purposes, you also have to assign at least one physical network adapter. You can allocate physical slots in any I/O drawer on the system.
Virtual I/O
Virtual I/O allows a server to support more partitions than it has slots for I/O devices by enabling the sharing of I/O adapters between partitions.
Virtual Ethernet enables a partition to communicate with other partitions without the need for an Ethernet adapter. A shared Ethernet adapter, supported by the Virtual I/O Server, allows a shared path to an external network. Virtual SCSI enables a partition to access block-level storage that is not a physical resource of that partition. With the Virtual SCSI design, the virtual storage is backed by a logical volume on a portion of a disk or an entire physical disk. These logical volumes appear to be the SCSI disks on the client partition, which gives the system administrator maximum flexibility in configuring partitions.
Minimum, desired, and maximum values
In a partition profile, specify three kinds of values for each resource. For memory, specify minimum, desired, and maximum values.
For processor, you define whether you use dedicated or shared processors.
If we chose to use dedicated processor, you can specify minimum, desired, and maximum values. For shared processors, specify minimum, desired, and maximum values for both processing units and virtual processors. For physical and virtual I/O slots, specify the required and desired values.
If any of the three types of resources cannot satisfy the specified minimum and required values, the activation of a partition fails. If the available resources satisfy all the minimum and required values but do not satisfy the desired values, the activated partition will get as many of the resources that are available.