Either way should be fine ... also, reseating the drive will probably change the status to something other than "unknown", starting a rebuild, showing the drive as failed ... or it could even remain unknown if that is the actual state of the drive, although this is not common.
I noticed today an odd state in the array attached to our CERC SATA 1.5/6ch. I say odd, because the Virtual Disk does not show as degraded. It shows as Ready and only when you click into the Array Disks do you see that one Array Disk 0:0 in this case shows as Unknown. This is a 4 drive RAID 5 without a hot spare. So the array is still ticking away, but i would certainly have expected it to be degraded. Perhaps it's the "unknown" part of it - but no indication that a rebuild or anything is being attempted. Anyway I can see over the past couple of days a few bad block errors, Event 2150. Message: Bad block extended medium error:  Array Disk 0:0 Controller 1, Connector 0Source Name: Server Administrator Time Written: 7/19/2012 8:00:40 AM EventType: Warning In OMSA I have no options to perform on the disk itself. "No Task Available." So I think the best course is to just replace the drive in question. And I can think of a couple ways to do that. 1. Down the server, take out the failed drive, replace with a new drive into the same position, or 2. Add replacement as a fifth drive, global hot spare, and look for a failover and rebuild after startup. But essentially leave the unknown disk in place for now. I'm sure there will be shades of difference in either of these two paths, along with possible gotchas, so I appreciate any feedback on how best to proceed. Thanks in advance.  
CERC 1.5/6ch best way to repl failed HD