Judging from the size of your VD (1.8TB = 4x500MB) and the fact that your VD MGMT screen shows 1 VD with 5 PD's ... you had not six, but five drives in a RAID 5 with the sixth set as a Hot Spare.  With this setup, when one drive dies, the Hot Spare automatically starts to rebuild in its place.  Once complete, the array shows as Optimal.  A replacement disk will show as Ready until you do something with it, like configure it as the new Hot Spare.
Hi there, I'm hoping someone may be of assistance on this. I have a Dell PowerEdge 2900 with a PERC 5i SAS RAID Controller. I have a 6-disk (6 X 500GB SAS drives) RAID-5 array built. A drive failed, and I ordered a replacement drive. I removed the failed drive, and inserted the new one. It did not automatically rebuild. I went into Dell's OpenManage interface, and saw the disk marked "foreign". I cleared the foreign status, but nothing happened (still showed as foreign). I decided to update to the latest firmware and driver. After rebooting, the foreign state had cleared, and the disk showed a status of READY. The array still wouldn't rebuild. I tried to add the disk into both the global and dedicated hotspare pools, thinking it would automatically start rebuilding, but it doesn't. I tried booting into the PERC BIOS, to try it from there. As you can see from this screenshot, the Virtual Disk thinks it is Optimal. But it is missing the physical disk (01:02). And this screenshot shows the physical disk in a Ready status, but the "Rebuild" option in the menu is greyed out. TL;DR - Somehow, my array is running degraded, but the controller is reporting that it is optimal, so i can't start a rebuild. Any ideas? I'm stumped. Thank you!
Dell PowerEdge 2900 - PERC 5i RAID Controller - Drive Failure, won't rebuild 
(array thinks it's optimal). Help?