Major updates affect many systems or require a significant system, network,
or service outage or touch a large number of systems. What is considered
large varies from site to site. For most sites, anything that affects
30 percent or more of the systems is a large update. Major updates include
upgrading the authentication system, changing the email or printer infrastructure,
or upgrading the core network infrastructure. These updates must
be carefully scheduled with the customer base, using a “push” mechanism,
such as email. Major updates should not be happening all the time. If they
are, consider whether you should change the way you are classifying some
updates. Some companies may want them performed at off-peak times, and
others may want all the major updates to happen in one concentrated maintenance
window (see Chapter 20).