This is something that I didn't know and it took a while to figure out how to fix without bricking a server.
I bought a Dell T310 server without the OS and installed SBS 2011 on it. I didn't think to erase the partitions that Dell put on it because they looked correct. What I didn't know (because it doesn't show or warn you) the OS partition that Dell created was formatted as FAT32. SBS installed without any problems (I blame Microsoft for this part). I was able to backup the system thinking I had good backups for a bare metal restore. When I went to test a bare metal restore the image was not found. This started a long process to troubleshoot and a few threads and help from others.
I solved the problem by adding a drive letter (B:) to the OS system partition.
Used an elevated DOS prompt and went to B:
Ran Convert B: /FS:NTFS
It converted to NTFS without destroying the boot information.
Removed drive letter B: from system partition.
Rebooted (I had to reboot to configure backup again).
Configured server backup and the system partition is now part of the bare metal backup (it did not show prior to this).
Bare Metal Restore now works!
My advice: Check your system partitions that's labeled OS or system reserved and see if it's formatted as FAT32. You will not be able to do a bare metal restore (BMR) if it is.