Sharing - a logical move for IBM's iSeries

E-mail your AS/400 product queries to [email protected], or by post to Nigel Adams, c/o IBM Computer Today, RH401, RBI,...

E-mail your AS/400 product queries to [email protected], or by post to Nigel Adams, c/o IBM Computer Today, RH401, RBI, Quadrant House, The Quadrant, Sutton, Surrey, SM2 5AS or by fax: 0181 652 8934

Question: I believe LPAR (logical partitioning), is to be made available on the iSeries/400. What benefits will this bring existing AS/400 users?
Answer: Logical Partitioning (LPAR) was first made available on the AS/400 with Version 4 Release 4 of OS/400. This capability is particularly useful for users who wish to consolidate multiple systems onto a single server. This is because it allows multiple partitions to be run on a single SMP system - and each of these partitions can have its own system values. Thus, if a customer is, for example, consolidating systems from multiple countries onto a single server in order to simplify operations and system management, one partition can be running an English language version of OS/400, a second a French version, another a German one and so on. There are also other scenarios in which LPAR can be useful - for example by running a test, or even a development environment, in a separate partition, while running live applications in the same system.

With the Version 5 Release 1 announcement that was made on April 23, there are significant enhancements to the LPAR capability that increase not only the flexibility of LPAR, but also the ease of use. Most (but not all) of the enhancements in LPAR support offered by V5R1 are available to AS/400 as well as to iSeries users.

The enhancement that is only available to iSeries users is Shared Processor support. This allows a part of a processor to be shared by multiple partitions. On AS/400 Models (ie 7xx range and earlier - these earlier models do not have the Istar or Sstar processor technology) even with V5R1, complete processor(s) must be allocated to each partition. On these models therefore the maximum number of partitions is 12 (on a 12-way model 740), and LPAR is not supported on uni-processors. On the iSeries Models with V5R1 you can now have up to 32 partitions on a single system, and you can also use LPAR on the 1-way Model 820 as well as the 1-way new Sstar processor on the Model 270. The maximum number of partitions that can share a single processor is four, but the smallest allocation that a single partition can have is .10 (one tenth) of a processor.

Other enhancements to LPAR supported by V5R1 are available on both iSeries and AS/400 Models. The most important of these is Dynamic Resource Movement. This allows memory, processors and interactive capability to be moved between partitions 'on the fly'. The movement of resources is extremely granular, allowing great flexibility of resource usage within a system. Thus in the case of processors, as little as .01 (one hundredth) of a processor can be moved between partitions - although this only applies to iSeries Models, and for AS/400s the minimum would of course be one whole processor. For memory as little as one megabyte can be moved between partitions and for interactive performance it is as little as 1 per cent of the interactive performance supported on the machine. This level of granularity coupled with the fact that these resources can be moved at any time without anything such as an IPL required means that the logical partitioning support of OS/400 is both powerful and flexible. In Version 5 Release 1 the management of logical patritions is enhanced so that this is all now done easily from GUI screens.

There are other benefits derived from all these enhancements, quite apart from the improved LPAR support itself. One is that with the support for Linux running in a secondary partition that has also been announced with V5R1, users can run Linux in a small partition on an iSeries system. The minimum for a Linux partition is .10 of a processor and 64MB of memory. This means that iSeries users who wish to use Linux for any applications such as perhaps as a Firewall, or for Print Serving or Web Serving, can if appropriate do so in a partition with a very small amount of hardware resource allocated to it. For users who wish to start looking at Linux, they will be able to do so in a very small secondary partition on an iSeries system with probably no additional hardware investment required. In this case the only cost would be the charge for purchasing Linux for the iSeries from one of the Linux distributors.

A second benefit is that the new support for processor sharing between LPAR partitions means that the uni-processor Sstar Model and 270 supports LPAR. This means that the complete iSeries range (with the exception of Model 270's which do not contain Sstar processors) supports LPAR. This functionality is brought much lower down the range that was the case previously. As a result even fairly small customers can look at using LPAR - to for example separate test and production environments on a single server.

Even prior to the recent Version 5 Release 1 announcement, the LPAR capabilities of OS/400 were amongst the most powerful available - particularly in the small to mid range marketplace. With this new announcement, and the ability to share processors between partitions on all iSeries models except the older model 270s, and the extremely flexible dynamic resource movement the LPAR capability is enhanced even further. Version 5 Release 1 is supported on all Risc Models of AS/400, and although these models do not support processor sharing. n

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