Red Hat SATELLITE 5.1.0 RELEASE NOTES Instrukcja Instalacji Pobierz pdf (Strona 30)

12 The Virtualization Cookbook for Red Hat Enterprise Linux 5.2

2.4 Memory planning

Planning memory may be the most difficult issue with z/VM and Linux on System z, but it is

the most important to ensure adequate performance. The simplest solution may appear to

involve having enough central memory (storage) in the LPAR so that z/VM never pages and

Linux never swaps. However, realistically such resource is often not available.

A useful rule of thumb is to allocate memory on a “just enough” basis for each Linux server. A

starting point is to set a virtual machine size by changing the memory allocation value at just

over the value at which the guest starts to swap at the Linux system level when under normal

loading. If some level of sustained swapping is inevitable due to the nature of the workloads,

then ensure virtual disks are used for the swap media.

An understanding of memory planning is recommended, and resources that cover this

important topic are listed here.

򐂰 IBM Redbooks publication Linux on IBM System z: Performance Measurement and

Tuning, SG24-6926:

http://www.redbooks.ibm.com/redpieces/abstracts/sg246926.html?Open

򐂰 IBM z/VM Performance Resource pages:

http://www.vm.ibm.com/perf/

򐂰 The IBM z/VM page specifically discussing memory allocation:

http://www.vm.ibm.com/perf/tips/storconf.html

One rule that can be recommended is to only have as few virtual machines logged on (or

disconnected) as possible to handle the workload being presented. Every virtual machine that

is not required should be logged off where appropriate, because this will mean more memory

for the other virtual servers that remain running.

2.5 Password planning

Secure passwords are critical to reliable security. However, requiring many different

passwords generally leads to people writing them down, which clearly detracts from security.

Sometimes it is difficult to balance these two extremes, especially when dealing with system

administration roles.

This book considers different system administration roles:

򐂰 The z/VM system administrator

򐂰 The Linux system administrator

򐂰 The Linux virtual server users

The z/VM and Linux system administrator may be the same person.

The method of backing up z/VM data onto the Linux controller means that the Linux

administrator will have access to all z/VM passwords. Therefore, the examples in this book set

all z/VM and Linux system administration passwords to the same value: lnx4vm. If the z/VM

and Linux system administrator roles must be kept separate and the Linux administrator is not

to have access to the z/VM passwords, then a different method of backing up z/VM data must

be chosen.

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Red Hat SATELLITE 5.1.0 RELEASE NOTES Instrukcja Instalacji Strona 30