Most systems administrators strive for consistent and reliable systems. Because any upgrade introduces unknowns into a system, you need to plan the upgrade process before unwrapping the CD-ROM.

You can upgrade from Exchange 4.0 (SP2 or later) or Exchange 5.0. The Exchange 5.5 administration program can operate on Exchange 4.0 and 5.0 servers, so if you have a network, you can upgrade one server at a time while continuing normal operations. However, you must upgrade MAPI clients (such as the standard Exchange client or Outlook) if you want to use certain user interface features (such as recovering deleted messages) in the new Outlook client 8.03.

You can upgrade your system in seven steps:

  1. Upgrade to NT 4.0 SP3. If you want to use Web clients, your server must run Internet Information Server (IIS) 3.0 (or a server running IIS 3.0 needs to be available to connect Web clients to Exchange).
  2. Make sure that any third-party software (e.g., fax connector or backup software) you use with Exchange is certified to run with Exchange 5.5. (Contact your vendor for this information.)
  3. Perform a full file-level backup of the Exchange information store, directory store, transaction logs, system Registry, and contents of all other directories Exchange uses. Some people use an online backup, but it might neglect to take a file-level backup of the contents of the Exchange directories and system Registry.
  4. Stop all Exchange services (optional). Use the EDBUTIL utility (which is replaced by the ESEUTIL utility in Exchange 5.5) to defragment the Exchange public, private, and directory stores. (You can perform this task a week or so before the upgrade.) This step ensures that the Exchange database's internal structures are as efficient as possible.
    As an added bonus, defragmentation will also return a lot of disk space to the file system. Efficient databases speed up the format conversion step in the upgrade process. However, you'll probably spend more time converting the databases with EBDUTIL than you'll save by being efficient. Nevertheless, I like taking this step because I can perform a routine maintenance task while the server is unavailable to users.
  5. Use the SETUP utility to perform the upgrade. Database conversion occurs early in the process.
  6. Verify that all the services have started after the upgrade is complete. For each client (e.g., MAPI, Web, IMAP4, or POP3), make sure that users can log on and can receive, read, and send email.
  7. Perform a backup.

You need to set a day aside to upgrade each server. The number of hours required to upgrade a server depends on several factors, including the version of Exchange that you are currently using, your hardware configuration, and the amount and type of data in the information store.

Whether you are upgrading from Exchange 4.0 or 5.0 makes a big difference in the time you will need to upgrade your system. Upgrading from 4.0 to 5.0 involves a database conversion. Therefore, if you move from 4.0 to 5.5 in one leap, you will need to do more work to build the internal structures. According to the release notes, moving from 4.0 to 5.5 takes about twice as long as moving from 5.0 to 5.5.

Your hardware configuration affects upgrade time. Converting a database involves reading pages from a source (the old store) and writing them into a target (the upgraded version of the store). Although CPU speed affects the rate at which Exchange 5.5 processes pages, the disk I/O subsystem's capability has a greater influence on the processing rate. If the disk I/O subsystem reads and writes data slowly, the database conversion will be slow. Thus, make sure that the Exchange databases are on the fastest possible device before you begin the upgrade.

The type and amount of data in the information stores influences upgrade time. Converting private stores usually takes much longer than converting public stores because of their different contents. Private stores tend to contain mailboxes, which often store many small items; public stores usually contain public folders, which often store several large documents. To speed the conversion, you can use Exchange's Mailbox Cleanup Agent in the Resource Kit to delete items in mailboxes before the upgrade.

Because Exchange doesn't provide any tools to analyze the contents of a store, predicting a store's level of complexity is difficult. Although you can use the ISINTEG utility and administration program to gather a few basic statistics (such as the number of mailboxes and space each mailbox uses), you'll probably end up using these simple calculations:

* If you are upgrading from Exchange 4.0 to 5.5, you can expect to process between 0.75GB to 1.25GB of data per hour.

* If you are upgrading from Exchange 5.0 to 5.5, you can expect to process between 1.25GB to 2.25GB of data per hour.

I have based these estimates on real-life upgrades. Keep in mind, however, that your upgrade time depends highly on your environment. So, use these estimates for planning purposes only.