We found the problem.  On the MD3220s, we noticed a few "unidentified host identifiers".  For reason unknown to us, the host port identifiers changed after we powered off and powered all R820s and MD3220s.  To fix the problem, we replaced the identifiers.  It seems as though someone swapped the SAS cables.  I do not think anyone did.  
We rebooted both our R820 ESXi 5.1 host and the SAS-connected MD3220 array.  After reboot, the HBA adapter on ESXi shows no devices.  We powered up the MD3220.  Waited for 5 minutes before powering up the R820.   FYI ... the full setup includes two R820 connected to two MD3220 via SAS.  Both R820 cannot see any devices on either HBA adapters after reboot.  We have redundant RAID controllers on the MD3220s and redundant HBA on the R820s. On the MD3220, the hosts interface Port status shows UP.   Have anyone seen this issue?  
ESXi 5.1 does not see any LUN after rebooting both MD3220 and R820