I need to back up a single server (Windows 2008 R2) onto an external drive. Because the server has millions of small files, block-level backup, not filesystem, is a requirement.
I can use Acronis Backup & Recovery, or Windows Server Backup. Is there any compelling reason to pick one over the other? (I already own the Acronis software, so price is not an issue.)
You did not identify the version of Windows. If it is 2008R2, then Windows Backup is almost a draw with its new backup format being that of VHDs. The VHDs can be mounted across Windows 7, 2008R2, Virtual PC, Hyper-V, etc.
The Acronis backup format can also be mounted "hot" onto a running system, but you need to install their drivers first. The bare-metal route still appears to be more streamlined on the Acronis side, but 2008R2 also has bare-metal capabilities as well.
I like the Acronis backup, but if you are on win2008r2, the backup software is very good, and fast.