Dynamic logical partitioning

DLPAR is available on POWER4–based System p systems with microcode updates dated October 2002 or later. It is possible to run a variety of partitions with varying levels of operating systems.

Prior to the enablement of DLPAR, you rebooted a partition to add additional resources to a system. DLPAR increases the flexibility of logically partitioned systems by allowing you to dynamically add and remove processors, memory, I/O slots, and I/O drawers from active logical partitions. You can reassign hardware resources and adjust to changing system capacity demands without impacting the availability of the partition.

You can perform the following basic operations with DLPAR:

• Move a resource from one partition to another
• Remove a resource from a partition
• Add a resource to a partition

Processors, memory, and I/O slots that are not currently assigned to a partition exist in a "free pool." Existing partitions on the system have no visibility to the other partitions on the system or the free pool. With DLPAR, when you remove a processor from an active partition, the system releases it to the pool, and that processor can then be added to an active partition. When a processor is added to an active partition, it has full access to all of the partition's memory, I/O address space, and I/O interrupts. The processor can participate completely in that partition's workload.

You can add or remove memory in 256 MB memory regions, or chunks. The effects of memory removal on an application running in an AIX® partition are minimized by the fact that the AIX kernel runs almost entirely in virtual mode. The applications, kernel extensions and most of the kernel use only virtual memory. When memory is removed, the partition might start paging. Because parts of the AIX kernel are pageable, this could degrade performance. When you remove memory, you must monitor the paging statistics to ensure that paging is not induced.

It is possible to add or remove I/O slots, such as network adapters, CD ROM devices, or tape drives from active partitions. This avoids the problem of having to purchase and install duplicate physical devices to accommodate multiple partitions when the device itself might not be used often. Unlike adding or removing processors or memory, the reconfiguration of I/O slots requires certain PCI hot-plug procedures prior to adding or removing a device in an active partition. Hot-plug procedures are available through SMIT.

The Hardware Management Console, or HMC, is attached to the system and allows you to perform dynamic reconfiguration (DR) operations. The HMC must be running R3V1.0 or later to support DLPAR. For a list of HMC operations relating to DLPAR, refer to Partitioning Implementations for IBM® eServer™ pSeries Servers.

The hypervisor is a thin layer of software which provides hardware management capabilities and isolation to the virtual machines (the partitions) running on a single physical system. Commands to control the movement of resources between partitions can be passed to the LPAR hypervisor via the HMC graphical user interface or through the HMC command line. You can only have one instance of the hypervisor running, and only the hypervisor has the ability to see and assign system resources. DLPAR does not compromise the security of a partition. Resources moved between partitions are re-initialized so that no residual data is left behind.