Sunday, August 22, 2010

Workload Management in AIX: WLM, DLPAR and now WPAR

Workload Manager - WLM
Over the years several methods of Workload Management have been developed as means to enhance resource utilization of systems. Some might say the Workload Management is a form of Performance Management – but that is only true in that Performance Management is actually Resource Management. In this sense, Workload Management is the collection of services and resource management applications that are used to monitor and regulate the resources a workload is permitted at any particular time.
Legacy UNIX systems had a very simple model of workload resource management. This was also known as sizing the box. Generally, the workload was the collection of all applications or processes running on the box. Various tools could be used – either system or application tools – to tune the application(s) to best fit the box. In other words, the amount of resources available to the workload was constant – whatever the box had.
With the release of AIX 4.3.3 in 1999 AIX included a new system component – AIX Workload Manager (WLM). This component made it possible to define collections of applications and processes into a workload, or workload class. A workload class was given resource entitlement (CPU, Memory, and starting with AIX 5.1 local I/O) in terms of shares. If there were four (4) classes active, and a resource was saturated (being used 100%) then AIX would compute a resource entitlement percentage based on the total active shares. If the four (4) classes had, respectively 15, 30, 45, and 60 shares the classes would be entitled to respectively – 10, 20, 30 and 40% of the resource concerned. As long as a resource was not constrained (less than 100% usage) WLM, by default, would not restrict a class resource entitlement.
The primary advantages of WLM are that it is included in the AIX base at no extra charge and is a software solution requiring no special hardware. However, performance specialists seem to have found it difficult to think in terms of performance management on a system which is regularly going to need more resources than it has. In other words, the legacy UNIX workload management model dominates most system administrations view of resource management.
Firmware Partitioning as Resource Management
Parallel with the development of WLM, a software solution for workload resource monitoring and control, the use of dividing a single system in to several separate system definitions commonly referred to as partitions. Virtualization in UNIX had become. Unlike WLM, partitioning required specific hardware features. For AIX, partitioning was introduced with the p690 POWER4 system.
Partitioning is a technique used to define multiple systems from a single system. A partition is allocated a specific amount of resources that it has to use as it desires. Individual partitions resources are isolated via firmare (Logical Partitions, or LPAR) or by the hardware component assembly (Physical Partition, or PPAR).
Initially, resource assignment was static. To change the resource allocation a halt and a (re)activation of the partition was required. Starting with AIX 5.2 the acronym DLPAR (dynamic LPAR) was introduced. This enhancement enables dynamic resource allocation to a partition, that is, a partition can have it's allocation of resources increased or decreased without a system, i.e. partition, halt and reactivation. With POWER5 the resource virtualization continued with the introduction of the firmware hypervisor, micropartitions, virtual Ethernet and virtual SCSI.
The advantages of partitioning are the flexibility in allocation of resources and the isolation quaranteed by the hypervisor firmware. However, partitioning requires specific hardware. Also, an administrator needs extra training to create and manage partition resources.
AIX 6.1 introduces Workload Partitions
A workload partition is a virtual system environment created using software tools. A workload partition is hosted by an AIX software environment. Applications and users working within the workload partition see the workload partition as if it was a regular system. Although less than a firmware created and managed partition – workload partition processes, signals and even file systems are isolated from the hosting environment as well as from other workload partitions. Additionally, workload partitions can have their own users, groups and dedicated network addresses. Interpprocess communication is limited to processes running within the workload partition.
AIX supports two kinds of Workload Partiions (WPARs).
A System WPAR is an environment that can be best compared to a stand-alone system. This WPAR runs it owns services and does not share writeable file systems with another WPAR or the AIX hosting (global) system.
An Application WPAR has all the process isolation a system WPAR has. The defining charactgeristic is that it shares file system name space with the global system and applications defined within the application WPAR environment.
Both types of WPARs can be configured for mobility to allow running insttances of the WPAR to be moved between physical systems or LPARs using the AIX Workload Partitin Manager LPP.
With the addition of WPAR (workload partitions) to AIX workload management has an intermediate level of flexibility and isolation of applications, users and data. Using WLM all process share the same environment with only CPU, memory and I/O resource allocation being managed when a resource is saturated. Firmware based virtualization of partitions starting with POWER4 hardware provides both hard allocation resource levels as well as complete isolation of services, network addresses, devices, etc. from all other partitions. Workload partitions, or WPAR, are a software based virtualization of partitions supporting a high degree of isolation and enhanced mobility over supporting global systems.

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