IBM DS8000 manual Building block, Physical partitioning Ppar, Logical partitioning Lpar

Building block

A building block is a collection of system resources, such as processors, memory, and I/O connections.

Physical partitioning (PPAR)

In physical partitioning, the partitions are divided along hardware boundaries. Each partition might run a different version of the same operating system. The number of partitions relies on the hardware. Physical partitions have the advantage of allowing complete isolation of operations from operations running on other processors, thus ensuring their availability and uptime. Processors, I/O boards, memory, and interconnects are not shared, allowing applications that are business-critical or for which there are security concerns to be completely isolated. The disadvantage of physical partitioning is that machines cannot be divided into as many partitions as those that use logical partitioning, and users can't consolidate many lightweight applications on one machine.

Logical partitioning (LPAR)

A logical partition uses hardware and firmware to logically partition the resources on a system. LPARs logically separate the operating system images, so there is not a dependency on the hardware building blocks.

A logical partition consists of processors, memory, and I/O slots that are a subset of the pool of available resources within a system, as shown in Figure 3-1 on page 46. While there are configuration rules, the granularity of the units of resources that can be allocated to partitions is very flexible. It is possible to add just a small amount of memory, if that is all that is needed, without a dependency on the size of the memory controller or without having to add more processors or I/O slots that are not needed.

LPAR differs from physical partitioning in the way resources are grouped to form a partition. Logical partitions do not need to conform to the physical boundaries of the building blocks used to build the server. Instead of grouping by physical building blocks, LPAR adds more flexibility to select components from the entire pool of available system resources.

Chapter 3. Storage system LPARs (Logical partitions) 45