[Version 5.0.1 and later]Tuning storage

Why and when to perform this task

WebSphere for z/OS puts much higher demands on virtual memory than a traditional workload. Ensure that you don't underestimate the amount of virtual storage applied to the WebSphere for z/OS servers. Generally, they use significantly more virtual memory than traditional application servers on z/OS or OS/390. Since real storage is needed to back the virtual storage, real storage usage may also be high.

Steps for this task

  1. Allocate enough virtual storage.
    The setting of REGION on the JCL for the proc should be large (at least 200MB to run), and much larger if high throughput is required. You can get an idea of the virtual storage usage through RMF or other performance monitors. It would not be unreasonable for the servant procs to specify REGION=0M, which tells the operating system to give all the available region (close to 2GB).

    Note: For more information on REGION=0M and IEFUSI, please see "Preparing the base OS/390 or z/OS environment" in the Getting Started section of the information center.

    If you choose to not put most of the runtime in LPA, as described in the program locations section, be sure to specify more region (as high as 512MB). Also, in conjunction with the increase in storage usage, you may have to define more paging space or auxiliary storage to back up the additional virtual storage used.

  2. (Optional)   Allocate enough real storage.
    Expect a requirement of at least 384MB of real storage for a small configuration. For controllers and servants, real storage utilizations depends on the size of the JVM heapsize.

    Recommendation: It can be the case that in a heavy use environment 2G of central storage is not enough to handle the real storage demands of a high volume Java application. In this case, we recommend that you configure with 64-bit real storage, which will give you the ability to dedicate more central storage to the LPAR. z/OS on a zSeries will always run in 64-bit mode. Running in 64-bit mode gives you the ability to define more than 2 GB of central storage When you configure for 64-bit real all of the storage is defined as central storage. For non-zSeries processors, or 31-bit mode, you can minimize paging by defining more expanded storage.

  3. Java virtual machine storage tuning tips for z/OS
    Also refer to Best practices for maintaining the run-time environment.

Related reference
Best practices for maintaining the run-time environment
Java virtual machine storage tuning tips for z/OS



Searchable topic ID:   tprf_tunezstorage
Last updated: Jun 21, 2007 9:56:50 PM CDT    WebSphere Application Server for z/OS, Version 5.0.2
http://publib.boulder.ibm.com/infocenter/wasinfo/index.jsp?topic=/com.ibm.websphere.zseries.doc/info/zseries/ae/tprf_tunezstorage.html

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