LPAR

In computing, a logical partition, commonly called an LPAR, is a subset of computer's hardware resources, virtualized as a separate computer. In effect, a physical machine can be partitioned into multiple LPARs, each housing a separate operating system.

The technology was initially developed separately by Amdahl, Hitachi Data Systems and IBM for the mainframe architecture ESA/390 in the mid 1980s, and continued also for zSeries and System z architectures. However, IBM later extended the idea to non-mainframe servers, such as pSeries since October 2001 [cite web |url=http://www.ibm.com/developerworks/eserver/library/es-susevio/ |title=POWER5 Virtualization: How to set up the Virtual I/O Server |accessdate=2008-09-25 |date=2005-06-29 |first=Nigel |last=Griffiths] and iSeries, albeit with varying technical specifications. Multiple operating systems are compatible with LPARs, including z/OS, z/VM, z/VSE, z/TPF, AIX, Linux (including Linux on zSeries), and i5/OS. In storage systems, such as the IBM TotalStorage DS8000, LPARs allow for multiple virtual instances of a storage array to exist within a single physical array.

Logical partitioning is performed mostly on the hardware layer. Two LPARs may access memory from a common memory chip, provided that the ranges of addresses directly accessible to each do not overlap. One partition may indirectly control memory of a second partition, but only by commanding a process of the second partition to directly operate on the memory. CPUs may be dedicated to a single LPAR, or shared between separate LPARs. While on Amdahl's MDF it was possible to configure an LPAR with both shared and dedicated CPUs it is no longer possible with mainframes.

On IBM mainframes, LPARs are managed by the PR/SM facility. Modern IBM mainframes operate exclusively in LPAR mode, even when there is only one logical partition on a machine. Multiple LPARs can form a Sysplex or Parallel Sysplex, whether on one machine or spread across multiple machines.

LPARs safely allow combining multiple test, development, quality assurance, and production work on the same system, offering several advantages such as lower costs, faster deployment, and more convenience. IBM mainframe LPARs are Common Criteria certifiable, equivalent to physically separate servers with no connections, so they are appropriate for the highest security requirements, including military use. Nearly all IBM mainframes run with multiple LPARs with the IBM System z9 and IBM System z10 supporting up to 60 LPARs.

References

See also

*Dynamic Logical Partitioning (DLPAR)
*Workload Partitions (WLPAR)
*HiperSocket, Hypervisor
*Virtualization
*Fujitsu XPAR
*SUN Dynamic Domains
*SUN LDOM