We have a RAID 5 setup (Megaraid SAS ROMB) with 4 930 Gb physical disks running as a 2.7 TB VD. Recently (a few months back) we had a drive fail and had to leave it in degraded mode for ages (various factors, wish we didn't but it's not in the scope of the question). We replaced the disk and rebuilt. The last few weeks we have noted persistent unrecovered medium errors on one of the physical disks - basically the same error that predated the first failure, and as frequently as right before it happened (roughly 5 incidences per minute logging 4-8 errors per incident). Thankfully budget is in a much nicer place right now, so we have a replacement disk ready.
The only problem, the only thing new to me here, is that we are performing the steps on an array which is still, as far as MegaRAID Storage Manager is concerned, Optimal. There's lots of information available around the place on replacing a disk in a degraded array (not to mention I would just be repeating the same steps I've done before) but I can't find any extra info on how to do it proactively, before the drive fails.
I believe that the process is essentially the same, with an added first step, but I'd really appreciate correction if I've missed the mark here:
In Storage Manager, mark the physical disk in question as offline (if I have the right end of the stick, this will cause the VD to go into degraded mode)
Turn off the computer
Replace the drive
Turn on the computer
Begin the rebuild
Now, how badly have I mangled those steps? (this might be worth noting, and is the reason for my double checking here, the computer is question is also the DC)