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Logical partition

From Alfawiki

A logical partition (LPAR) represents a division of a computer's physical hardware, virtualized to function as an independent system. A single physical server can be segmented into several LPARs, each operating its own distinct operating system instance.

History

IBM was the forerunner in developing hypervisor technology through virtual machines, initially with CP-40 and CP-67, and later introduced the Virtual Machine Facility/370 for the S/370 in 1972. The company enhanced virtualization capabilities in 1983 by adding the Start Interpretive Execution (SIE) instruction on the IBM 3081 within the 370-XA framework.

In 1982, Amdahl Corporation introduced its Multiple Domain Facility (MDF). IBM responded in 1988 with PR/SM (Processor Resource/System Manager) on the ESA/370 architecture using IBM 3090 processors. PR/SM is a type-1 Hypervisor that allows multiple LPARs to share CPUs, memory, I/O channels, and LAN interfaces; it also enables shared access to DASD devices. PR/SM remains a core component of all IBM System z platforms, where LPAR denotes both the operating mode and individual partitions.

Further development of MDF-based LPARs continued by Amdahl and Hitachi Data Systems, utilizing ESA/370 capabilities such as access registers for managing multiple data spaces. IBM advanced LPAR technology with its 64-bit System z platform, introducing dynamic reconfiguration features that permit changes to channel paths and devices without requiring partitions to reboot.

With the IBM z13 and first-generation LinuxONE servers, IBM launched the Dynamic Partition Manager (DPM), providing web-based tools for configuring and overseeing LPARs. The z/VM operating system supports z/Architecture HiperSockets, facilitating high-speed TCP/IP communications among virtual machines and LPARs on the same server through Queued-Direct Input/Output (QDIO).

LPAR technology also extended to IBM Power Systems: initially implemented on PowerPC-based AS/400 (later iSeries) in 1999 and pSeries servers in 2001, these platforms employ PHYP (POWER Hypervisor) starting from the POWER4 generation to enable LPAR functions. Supported operating environments include mainframe systems like z/OS, z/VM, z/VSE, and z/TPF; Power Systems’ AIX and IBM i; as well as various distributions of Linux.

In storage solutions, IBM TotalStorage DS8000 arrays utilize LPARs to partition a single physical array into multiple virtual storage instances.

Other manufacturers have incorporated LPAR support: Fujitsu introduced x86-64 PRIMEQUEST servers with LPAR capabilities in early 2010; Hitachi followed by releasing CB2000 and CB320 blade systems supporting LPAR on x86-64 architectures in late 2011.

Hardware partitioning

Logical partitioning involves dividing hardware resources among partitions. Two LPARs can share memory from the same chip if their address spaces do not intersect. One partition may indirectly control memory allocated to another through an intermediary mechanism. CPUs can be assigned exclusively or shared among LPARs; while Amdahl’s MDF permitted configurations combining shared and dedicated CPUs within an LPAR, this is no longer feasible on contemporary mainframes.

On IBM mainframes, management of LPARs is handled by the PR/SM facility or the streamlined Dynamic Partition Manager (DPM). All current 64-bit IBM mainframes—except early models like the z900 and z800—operate solely in LPAR mode even when only one partition is active. Multiple z/OS partitions can be grouped into a Sysplex or an Parallel Sysplex, whether residing on a single machine or distributed across multiple systems.

For IBM System p POWER hardware, PHYP (the POWER Hypervisor) manages LPARs, functioning as a virtual switch that facilitates virtual SCSI communication between partitions. Introduced with the POWER5 processor, Micro-Partitioning allows up to ten times more LPARs than physical processors by allocating fractional CPU shares. All IBM systems from POWER5 onwards support partitioning. PowerVM-enabled System P servers permit shared CPUs to contribute unused processing cycles into a shared pool; however, dedicated processors cannot be shared. These idle cycles are then available to other partitions according to configurable policies. Dynamic Logical Partitioning enables resource adjustments without rebooting partitions. PowerVM is a licensed feature enabling virtualization on POWER4 through POWER7 and subsequent servers.

Using technologies like Intel vPro and features such as Non-uniform memory access, Logical Partitioning implementations are also present on Intel Xeon platforms offered by vendors including Hitachi Data Systems.

When properly certified, LPARs allow consolidation of testing, development, quality assurance, and production workloads onto a single server, reducing expenses and speeding deployment cycles. IBM mainframe LPARs achieve Common Criteria EAL 5+ certification—equivalent in security to physically isolated servers—supporting stringent security requirements including military applications. The vast majority of IBM mainframes run multiple LPARs concurrently; for example, the IBM System z9 and IBM System z10 models support up to 60 partitions, with newer versions accommodating as many as 85.

See also

External links

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