On 8/30/06, John Campbell <[EMAIL PROTECTED]> wrote:
The hell of it is that I *don't* have a zSeries-- or even an instance within z/VM-- where I can run Linux, so I can only do some speculation.
Yes, and that is where it makes a difference. On discrete servers it may make sense to tune your configuration for maximum single server performance. Any resources that you don't use are wasted anyway, and there's nothing wrong to increase CPU usage from 10% to 20% if that buys you 10% more throughput. Your tuning is not complicated by other things happening on the same machine (although a shared disk system like a SAN is going to impact your tuning if the bottleneck is other than on your own doorstep). With Linux on z/VM the tuning objective often is to achieve lowest cost per transaction (as long as you meet the required response time). It is very rare that you need to size your virtual machine to consume all available resources of the entire machine (like CPU or I/O). In most cases the z/VM system will also run other virtual machines at the same time and normally your objective is to have all of them make some progress rather than let one virtual machine run away with the system. Oversized systems then require extra monitoring to prevent them from taking all that you gave them. Even on a mainframe you will not be happy with a Linux server constantly swapping to disk. If you're swapping so much that you would enjoy multiple paths to your swap devices, there's probably something wrong in your setup. The only good thing of swapping to real disk is that you slow down the server enough to prevent it from taking up a lot of resources. Swapping to VDISK however is very fast and is a good trade-off to fool Linux memory management. Things like CMM let us fool Linux even better, and if you can steer that with the system wide performance metrics from z/VM it can be very effective. Rob -- Rob van der Heij Velocity Software, Inc http://velocitysoftware.com/ ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
