Um,... I found out. It's in Appendix B of the manual for the S100. RTFM, right?
When a system is booting, the PERC S100 virtual disk manager displays the status of disks connected to the system. The indications can be, among others: DEGRADED NORMAL READY We have a T110 server with 3 hard drives attached. One is a non-RAID virtual disk holding the operating system (Windows Server 2008 R2). The other two drives are configured as RAID 1, and hold only data. We want to replace those RAIDed data drives with larger ones. We won't be touching the OS non-RAID drive. The S100 says that the status of the existing RAID is "NORMAL (R/W)". When I replace the hard drives in that array and configure a new RAID array with the new drives, the status is "READY (R/W)". Unfortunately, when the system boots, it gets stuck in a reboot loop until I put the original drives back. The only clue I have is that difference in the boot time status of the RAID. There is nothing in the OS's logs to indicate what the problem might be. Does anyone know the exact meaning of those status messages? 
Dell PERC RAID status indicators