The SBS 2011 Essentials installation is a highly automated installation that is quite reliable, but there are some areas that can cause issues. The known issues are:
Hard disk too small or not recognized.
Network card not found.
SBS 2011 Essentials requires a hard disk of at least 200 GB for the primary hard disk, and if it can’t find that hard disk during initial installation, the installation will fail. The most common cause of this is that the drivers for the primary disk aren’t included in Windows Server 2008 R2, and therefore the disk isn’t visible to the installer. Before the installation can proceed, you need to add the missing drivers.
To add drivers during the installation, click the Load Drivers ...