Chapter 8. Load Generation and Testing

There are a great many variables to account for in building and tuning a highperformance email server. Because of the many variables and because much of the information available from hardware and software vendors cannot be easily incorporated into a model that will accurately predict the real-world capacity for any configuration, the only way to gain any confidence in how much email a server can process is to set it up and see how it performs in practice.

Obviously, several problems arise with this strategy. First and most important, no matter how much preparation and planning one does, very real risks will always arise in replacing one operating server that holds critical data with another server. Moving the data from one repository to another is always perilous. If the new server configuration doesn't perform adequately, then the data may need to be moved back to the original machine and then again to another new server configuration, with no guarantee that another configuration will perform any better.

Every equipment substitution in the upgrade process creates a window of downtime. In some roles in some environments, this process can be relatively pain-free. For example, if an organization plans to replace the email gateway responsible for relaying email through their firewall, and that organization can tolerate a few hours of deferred incoming and outgoing email during nonwork hours, then the cost of having to perform any particular upgrade is likely to be rather small.

In other situations, any outage window, no matter how small or well coordinated, can be expensive. For example, if one needs to replace a server that holds an email message store for a large ISP, doing so will be expensive by some measure. The customers will expect the server to operate on a 24/7 basis, and no matter how diligently an organization works to inform the customer base about the impending outage, some people will inevitably not get the message, ignore it, or forget they received it. When they go to retrieve or send email and find that they cannot, it will cost the ISP real money. Every outage will generate calls to customer support, which consumes personnel time, telephone resources, and customer goodwill. Therefore, in this sort of environment every effort should be made to ensure that any particular upgrade takes the minimum amount of time and has the maximum chance of achieving its goals.

The best way to obtain confidence in a new solution is to test and tune that configuration prior to going live with it in as realistic an environment as one can manage. This chapter discusses the issues involved in designing a test system as well as the difficulties in making a test system approximate real-world use as closely as possible.



sendmail Performance Tuning
sendmail Performance Tuning
ISBN: 0321115708
EAN: 2147483647
Year: 2005
Pages: 67

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