  You should NEVER do this.  Import is for RAID configurations that are failed/offline (2 drives foreign in a RAID 5, for example).  Clear is when a single disk's configuration was marked by the controller as foreign, AND the array is up and running.  Importing a foreign configuration when the array is up and running is a very fast way to corrupt/destroy data.   Number of slots and "hot spare option" are not related.  If your replacement drive shows as foreign, you need to first CLEAR the foreign configuration, THEN assign it as a Hot Spare to start the rebuild. Force the drive offline first, then pull it HOT, then insert the replacement after 30 seconds or so.  Never shut down a server to replace a hot-swappable drive.
Several months ago, I had 1 of the 4 drives go to a SMART status = bad.  Tried several times to replace the drive using BIOS and Server Manager.  Couldn't get the server to replace the drive.  Tried updating controller firmware, etc. The options I needed to replace or rebuild simply were not available.  Note that I have only 4 slots and all 4 slots are used, so I didn't want to use the Hot Spare option.  So, I had to keep reimporting it as a foreign drive even though the SMART status was bad.  I gave up and figured that I would just wait for the drive to fail. Now, the drive has failed has a flashing amber light.  I've scheduled to replace the drive on Friday.  It is a  Perc 6/i controller.  I've done several other  RAID driver replacements with no issues.  But, not Dell/Perc.  Can I simply pull the bad drive and plug the new one in?  Or, should I shut the server down first?  What's the best way to replace the drive?  I do have a current backup, but would prefer not to have to use it.  Server is running Windows 2008 Standard 64-bit.
Poweredge R410 hard drive failed on RAID 5