Windows Server 2008 provides an in-place upgrade option for installing the new OS on
an existing server. Unlike a clean installation, an in-place upgrade keeps files, settings,
and programs intact while the OS is upgraded. In general, an upgrade is a more complex
process than a clean installation, and it requires some careful preparation (e.g., reviewing
application compatibility information, backing up the server’s data and configuration information,
including boot and system partitions and system state data) ahead of time.
The Server 2008 upgrade option is supported from Windows Server 2003 SP1 or later
versions of the OS but only in limited scenarios. Cross-architecture upgrades are not supported.
For example, you can upgrade a 32-bit Windows 2003 server to 32-bit Server 2008
and an x64-based Windows 2003 server to x64-based Server 2008, but you can’t upgrade
a 32-bit Windows 2003 server to x64-based Server 2008. Upgrades from Windows 2003
for Itanium-Based Systems to Server 2008 for Itanium-Based Systems are not supported,
and you cannot upgrade from any OS to a Server 2008 Server Core installation; Server Core
is always a new installation or an in-place upgrade on itself. No in-place upgrade path exists
from Windows Server 2000 or Windows NT Server to Server 2008.
Upgrades are really only practical for Windows 2003 systems running OS components
and nothing else. Just because the OS can be upgraded doesn’t mean that the software running
on the server will support an OS upgrade process. For example, Exchange Server 2007
SP1 will run on Server 2008, but Microsoft will not support an in-place upgrade of x64-based
Windows 2003 to x64-based Server 2008 with Exchange installed. I had an antivirus program
that ran fine on a Windows 2003 system cause a problem. After I upgraded to Server 2008,
the antivirus software wouldn’t let the server boot because the driver was unsigned.
The reasons for such problems are numerous, but a key reason is that Server 2008 is an
image-based installation. With Server 2008, you cannot “upgrade” in the traditional sense of
replacing OS files and updating components. Instead, you essentially have to break down the
existing system into “the OS” and “everything else” (e.g., files, registry settings, component
registration), shove all of it into a backup folder, lay down the Server 2008 image on the
system, put back the “everything else,” and finally look at the installed Windows components
and work out which Server 2008 roles and features those components equate to.
To further complicate matters, some server roles require special handling. For example,
if you want to upgrade a Windows 2003 domain controller (DC) to Server 2008, you must
first prepare the Active Directory (AD) forest and domain for the introduction of a Server
2008 DC. To do this, you use the Adprep command-line tool (located on the Server 2008
installation disk in the \sources\adprep folder), which extends the AD schema and updates
permissions as necessary so that the domain can support a Server 2008 DC. (For more
information about the Adprep tool, see technet2.microsoft.com/windowsserver2008/en/library/aa923ebf-de47-494b-a60a-9fce083d2f691033.mspx?mfr=true.)