1. If nrpos <= 1, don't output rpos table (and set fs_cpc to 0) - disabling the use of the rotational position table.
2. Allow specification of 0 rotational positions (disables function).
3. Make rotdelay=0 and nrpos=0 by default.
   
   The purpose of the above is to optimize for modern SCSI (and IDE) drives

that do read-ahead/write-behind.