If you run Microsoft Exchange Server version 5.5 Setup on a server that is running Microsoft Exchange Server version 4.0 or version 5.0, you have the option of upgrading rather than reinstalling your server. Upgrading is a more extensive process than reinstalling because upgrading reformats the information store and directory databases for version 5.5.
When Setup upgrades the databases, it upgrades them sequentially. Databases are upgraded before files are copied from the compact disc. For example, if you are upgrading a Microsoft Exchange Server computer from version 4.0 to version 5.5, Setup performs the following steps:
When you upgrade your server from version 5.0 to version 5.5, Setup performs only steps 3, 4, and 5.
When you run Setup, you can choose to perform a standard upgrade or a fault-tolerant upgrade.
Standard upgrade If you are performing a standard upgrade, Setup copies the new databases over the old databases in their current location. This option requires less disk space than a fault-tolerant upgrade, but it is more risky. If Setup fails while the databases are being upgraded, all data is lost and you must restore the server from a tape backup.
Fault tolerant upgrade If you are performing a fault-tolerant upgrade, Setup copies the existing databases to a new, temporary location on the server's local disk. When all database files have been upgraded to version 5.5, they are copied back to the original location. This option is safer than a standard upgrade because data is not lost if Setup fails while the databases are being upgraded. However, the fault-tolerant upgrade requires more available disk space on the Microsoft Exchange Server computer than a standard upgrade.
Note The fault-tolerant upgrade option is available only when you upgrade from Microsoft Exchange Server version 5.0 to version 5.5.
Upgrade Disk Space Requirements
Disk space requirements vary depending on the type of upgrade you are performing. Neither option performs a complete backup of your existing databases. You should perform a full backup of your information store before running Setup.
Note Before upgrading your server you should back it up.
Standard upgrade A standard upgrade requires available disk space approximately equal to 17 percent of the largest database you are upgrading.
Fault tolerant upgrade A fault-tolerant upgrade requires enough available disk space for all of the databases combined. For example, if you are upgrading a 10 megabyte (MB) private information store, a 20 MB public information store, and a 10 MB directory, you must have at least 40 MB of available disk space on the disk that you specify as the temporary upgrade location.
What to Do If Setup Fails While Upgrading
If Setup fails while you are upgrading your Microsoft Exchange Server computer, take one of the following courses of action, depending on what upgrade option you have chosen.
Standard upgrade If you are performing a standard upgrade and Setup fails during the first stage of the upgrade when the databases are being upgraded, you must restore Microsoft Exchange Server from a tape backup.
If Setup fails while files are being copied from the Microsoft Exchange Server compact disc to the local disk on the Microsoft Exchange Server computer, rerun Setup. Setup usually finishes copying the required files and completes the setup process successfully.
Fault-tolerant upgrade If you are performing a fault-tolerant upgrade and Setup fails during the first stage of stage of the upgrade when the databases are being upgraded, you can restart the server using the previous installation of Microsoft Exchange Server.
If Setup fails while the databases are being copied from the temporary location to the location of the previous installation, rerun Setup.
If Setup fails while files are being copied from the Microsoft Exchange Server compact disc to the local disk on the Microsoft Exchange Server computer, you should rerun Setup. Setup usually finishes copying the required files and completes the setup process successfully.