The real reason for ensuring a hierarchy of storage in z/VM is to meet the objective of paging less to DASD.
The page stealing algorithm used to take pages from main storage is not as efficient as the LRU algorithm for moving pages from Expanded Storage. Memory constrained systems found that their external paging rate dropped when they converted some real storage to expanded. The stealing algorithm steals a lot of the wrong pages, often taking needed pages and moving them to dasd. bad. Sure moving pages back and forth between expanded and real cost CPU - but paging to disk is orders of magnitude worse. >Rob van der Heij <[EMAIL PROTECTED]> writes: >> Yes, in your configuration you should define expanded storage. It's >> for providing a hierarchy in storage management as well as a >> circumvention to reduce the impact of contention under the bar. >> Especially when the total active memory of your Linux server is >> getting close to 2G (and unless you do things, eventually the entire >> Linux virtual machine main memory will appear active to VM). >> 25% has been suggested as a starting point, but measurements should >> help you determine the right value. The right value depends a lot on >> what Linux is doing. And make sure to disable MDC into expanded >> storage as I suggested yesterday. > >note if you have 16gbytes of expanded store and 16gbytes of regular >storage ... then only stuff in the 16gbytes of regular store and be >used/executed. stuff in expanded store has to be brought into regular >store to be accessed (and something in regular store pushed out >... possibly exchanging places with stuff in expanded store). > >if you have 32gbytes of regular store ... then everything in regular >store can be directly used/executed ... w/o being moved around. > "If you can't measure it, I'm Just NOT interested!"(tm) /************************************************************/ Barton Robinson - CBW Internet: [EMAIL PROTECTED] Velocity Software, Inc Mailing Address: 196-D Castro Street P.O. Box 390640 Mountain View, CA 94041 Mountain View, CA 94039-0640 VM Performance Hotline: 650-964-8867 Fax: 650-964-9012 Web Page: WWW.VELOCITY-SOFTWARE.COM /************************************************************/
