Several options are available for upgrading your existing Exchange servers to Exchange 2000. They are:
Important You must install Windows 2000 Server to run Exchange 2000 Server. If you are using Windows NT 4.0 Server, you must upgrade the operating system to Windows 2000 Server.
With Exchange Server 5.5 SP3, you can simply upgrade the databases. This requires taking the server offline and then running the Exchange 2000 Server Setup program.
The advantages of an in-place upgrade are that existing hardware can be used, and the existing data in the information stores is converted very rapidly, at approximately 8 GB per hour. This makes the upgrade process extremely fast. The speed of the database conversion depends on the number of folders that exist, and not on the total amount of data stored. The reason for this is that most of the upgrade time is spent by the access control list (ACL) upgrade process, which replaces Exchange directory access control entries with objects from Active Directory.
The disadvantages of an in-place upgrade are that the server must already be running Windows 2000 and Exchange Server 5.5 and the hardware must be capable of running Windows 2000 and Exchange 2000. Additionally, in-place upgrades may require more user downtime than other migration methods.
This upgrade method involves installing Exchange 2000 Server on new hardware, joining the existing Exchange site, moving the data to Exchange 2000 Server, and then decommissioning the old servers. Many companies use this migration method because it provides a good opportunity to update their hardware and software.
The advantages of the move mailbox upgrade method are minimal user disturbance; the only downtime is the time it takes to move the users' mailboxes; users can be directly upgraded on Exchange Server 4.0 and 5.0; connectors can be upgraded simply by moving them to the server running Exchange 2000; no operating system or Exchange upgrade is required on the existing server; and not all users on an existing server must be moved at the same time.
The disadvantage of the move mailbox upgrade method is that it can be difficult to justify the cost of new servers when your existing Exchange servers may already meet the hardware requirements for Exchange 2000 Server.
The leapfrog upgrade method is like a double upgrade. Essentially, a large company can purchase one or two new servers to upgrade their entire mail system. The move mailbox method is used to move data to the new servers. Then the older Exchange servers are upgraded to Exchange 2000 Server, verified as stable, and the data is moved back again.
This upgrade method works best if the data you need to move is in mailboxes and public folders. If you currently have dedicated servers for these roles, you may want to use this method to convert user data and use the in-place upgrade method to upgrade Key Management System, connector, and bridgehead servers, because these do not directly impact user access to Exchange data.
The advantages of the leapfrog upgrade method include those of the move mailbox upgrade method. Additionally, you can use existing hardware and the new hardware you will need for the migration is minimal.
The disadvantages of the leapfrog upgrade method are that the server names change as users are moved to new equipment, foreign connectors and other components are difficult to move, and the migration is slightly more difficult to plan and execute.
For more information, see Microsoft Exchange 2000 Server Planning and Installation.