After plugging in a third scsi drive, cfdisk could not see /dev/sdc. mke2fs also could not see the /dev/sdc. It was important to me not to have to re-boot to get the drive recognized.

By asking around in freenode.net IRC channels I got the clue that the scsi bus needed to be re-scanned. I installed scsitools but could not find a rescan as part of that. It was suggested to get the afacli from Dell:

http://linux.dell.com/storage.shtml#megaraid but this did not work for me. After installing Alien in order to install the RedHat rpm Dell supplies on my debian box, the cli ran fine but didn't see any compatible controller on my system.

The solution turned out to be a bash shell script from sourceforge:
http://scsi-rescan.sourceforge.net/

Be very careful if you have a scsi device as your boot disk. I carefully used the shell script to determine the likely number for my third added drive (2) and rescanned only that scsi ID.

As the instructions relate, if I had rescanned all or scsi ID 0 - that would have affected my boot drive.

It took some time for the rescan shell script to find and recognize the new drive. After that, cfdisk worked as expected and mke2fs also worked as expected.