Dynamic Logical Partitioning
Dynamic Logical Partitioning (DLPAR), is the capability of a logical partition (LPAR) to be reconfigured dynamically, without having to shut down the operating system that runs in the LPAR. DLPAR enables memory, CPU capacity, and I/O interfaces to be moved nondisruptively between LPARs within the same server.
IBM introduced DLPAR on POWER4-based servers with the availability of AIX 5.2 in October 2002. DLPAR is now supported by the operating systems AIX and i5/OS. The Linux kernel for POWER also supports DLPAR, but dynamic reconfigurations are limited to CPU capacity and PCI devices, but not memory. The fundamentals of DLPAR are described in the IBM Systems Journal paper titled: Dynamic reconfiguration: Basic building blocks for autonomic computing on IBM pSeries Servers ( http://www.research.ibm.com/journal/sj/421/jann.html )
Later on, the POWER5 processor added enhanced DLPAR capabilities, including micro-partitioning: up to 10 LPARs can be configured per processor, with a single multiprocessor server supporting a maximum of 254 LPARs (and thus up to 254 independent operating system instances).
There are many interesting applications of DLPAR capabilities. Primarily, it is used to build agile infrastructures, or to automate hardware system resource allocation, planning, and provisioning. This is turn results into increased system utilization. For example, memory, processor or I/O slots can be added, removed or moved to another LPAR, without rebooting operating system or even application running in an LPAR. IBM DB2 is such application (http://www.ibm.com/developerworks/eserver/articles/db2_dlpar.html), it is aware of the DLPAR events and automatically tunes itself to changing LPAR resources.
The System z9 and zSeries mainframes and their operating systems, including Linux on zSeries, support even more sophisticated forms of dynamic LPARs. Relevant LPAR-related features on those mainframe platforms include Intelligent Resource Director, Sysplex, Parallel Sysplex, Geographically Dispersed Parallel Sysplex, and Hipersockets. The System z9 supports up to 60 LPARs on a single server, but mainframes also support an additional level of virtualization using z/VM with the ability to support thousands of operating system instances on a single server.