Chapter 2: Capacity and Availability Management 15
To deal with this problem, you should continually monitor available disk space on your
servers running Exchange. If the RAID array containing the stores gets close to half full, an
alert should be sent indicating the problem, and that the Exchange Database might need to
be defragmented offline. To do this, perform an alternate server restore (see Chapter 5 for
details) and then defragment the database on this alternate server. If this is successful and
results in a significant reduction in database size, you can perform the defragmentation at
the next scheduled maintenance time.
Performing the alternate server restore also has the advantage of ensuring that your backup
and restore procedures are working effectively. You should check this regularly in any case.
This is also covered in more detail in Chapter 5.
Probably the most important thing to remember when performing capacity planning is to
size conservatively. Doing so will minimize availability problems, and the cost reduction
will generally more than compensate for any excess capacity costs.
As well as looking at technical issues, you will need to examine staffing levels when you
are capacity planning. As your Exchange 2000 environment grows, you might need more
people to support the increased load. In particular, if there are more users requiring
increased services, there is likely to be a greater need for help desk support.
Availability Management
Availability management is the process of ensuring that any given IT service consistently
and cost-effectively delivers the level of availability required by the customer. It is not just
concerned with minimizing loss of service, but also with ensuring that appropriate action is
taken if service is lost.
One of the main aims of Exchange 2000 operations is to ensure that Exchange is avail-
able as much as possible and that both planned and unplanned interruptions to service are
minimized. Availability in an organization is typically defined by your SLAs in two
ways—service hours and service availability.

Service Hours

These are the hours when the Exchange services should be available. Typically, for a large
organization this will be all but a very few hours a month. Defining your service hours
allows you to create defined windows when offline maintenance of your servers running
Exchange can be performed without breaching the terms of your SLA.
You might choose to define in the SLA the exact times when Exchange services might be
unavailable. For example, you might state that Exchange services might be unavailable for
four hours every first Saturday of the month. However, in large organizations it is often
more practical to commit to, for example, no more than four hours of scheduled downtime
per month, with a week’s notice of any scheduled change. This allows changes to be made
much more easily across the organization, at times when the right staff can be devoted to
the tasks.