Alex, It may be that you are using an older version of OMSA or that the controller is out of date. With the drive not going offline.What you can do is power the server off, once it is powered down then remove the drive. Power up with nothing in that slot, the array should show as degraded. Insert the replacement drive and it should start to rebuild.  Let me know how it goes.
Hi, Hopefully a quick and easy solution to this as I'm procrastinating at the moment. Have a Poweredge 1800 (PERC 4/SC, RAID5) and got a predicted failure on one of the SCSI drives. It's hot-swappable and we've got the replacement. However, OpenManage is not allowing me to set the failing drive to 'offline' so that I can swap it out. I'll choose the offline option from the dropdown and when executing it just blank screens (see picture). Is this a sympton of something not quite right? No problems with other options (blink/unblink). Alternatively can I just boot into the PERC menu, set the current drive offline, swap out, set new drive to rebuild from there? Appears to be a split opinions when I look at other similar issues on other forum threads i.e. some say you should just pull the drive and swap it even without setting it offline first. thanks, Alex  [IMAGE]
Need to replace drive but OpenManage not allowing failing drive to be set to 
'Offline'