On Mon, May 11, 2009 at 5:20 PM, Ross Johnson <[email protected]> wrote:
> According to the z/VM and Linux SLES SP2 Cookbook, a ratio of 3:1 of central > to expanded storage is recommended, further justified at > http://www.vm.ibm.com/perf/tips/storconf.html. Improvements documented with > z/VM 5.2 suggest that a maximum of 2G expanded is recommended, or 25 % of > all configured storage. In my z/VM 5.4 and SLES SP2 implementation, I have > been informed that expanded storage is no longer required for z/VM with > Linux guests. I tend to believe the latest change in 5.2; a 4:1 ratio up to > a max of 2G expanded. Any suggestions? When you over commit memory you need expanded storage, also with z/VM 5.4. There is no fixed maximum as what is useful. The required amount depends on configuration and workload. Within reasonable limits, there's little penalty for too much expanded storage. But there's heavy penalty for too little expanded storage. It's comparing apples and oranges. Before z/VM 5.2 there were specific workloads that would only run with very large amount of expanded storage. Those issues have been addressed and those workloads don't need it anymore. But we're now 3 years further and people run different workload and configurations have changed. Many of these configurations benefit from expanded storage. PS We're talking about expanded storage used by z/VM for paging. Not expanded storage attached to the guest (as some examples in the Novell documentation seems to suggest). It does not make sense to attach expanded storage to Linux guests for swap, it never did. Rob -- Rob van der Heij Velocity Software http://www.velocitysoftware.com/
