You can and you should hot-swap the faulty one for a replacement.  Never power down a server with hot-swap drive to swap a drive ... "if it is hot-swap, swap it hot".
I have a Dell 2650 & this morning the Dell open manager reported failure on one of the disks.Critical;Physical Disk 0:0;Failed;No;Available Tasks;;SCSI;0.00GB;0.00GB;0.00GB;No;SEAGATE ;ST336753LC      ;DX10;3HX34W7D;320;320There are other disks as well which are online. Can I hot swap the faulty one?
Disk 0:0 Failed