4.7 failed disk - help!

• • Hi,
     
    Sorry for posting a question about version 4.7 here but there doesn't seem to be anywhere else to post.  My UnRAID system has been happily working away perfectly for the past 4+ years but I just looked at the console by chance and noticed that I have a failed disk.    Annoyingly I got no email alerts as it looks like GMail have recently (and silently!) changed their security and now blocks my UnRAID box!  I wondered what the "unauthorised login attempt blocked" emails were - anyway, I've fixed that problem on Gmail and now need to fix the UnRAID box.
     
    You'll have to forgive the stupid questions as I've forgotten almost everything I learned about UnRAID simply because it's been running faultlessly for so long.  I can't even remember the root login so I can only access the console on port 8080 (the "unRAID Main" console on port 80 asks for a login and I can't remember what it is!).  I have 1 parity disk and 2 data disks, the console is showing "DISK_DSBL" on the second data disk.  I will try shutting the box down and reseating the disk in case it's a connection problem, but the machine is an HP Microserver which sits out of the way behind the sofa and is unlikely to have been knocked, etc.  Also the drives sit in a cradle with direct connections to a backplane - no SATA cable.
     
    A few questions:
     
    
    • If I simply stop the array, shut down the box, replace the second data drive and restart will it rebuild the failed second data disk onto the new drive?  Do I need to preclear the new disk or anything?
      
    • I vaguely remember some issues with Western Digital EARS drives needing aligning or similar.  Is there any issue with the current WD drives (e.g. WD20EZRX)?
      
    • How can I reset the root password?
      
    • I think I read that 4.7 can only use 2tb disks max - is that correct?  I would have liked to have put a larger drive in as parity to give me more options for increasing capacity in the future but don't want to mess around upgrading UnRAID versions while I have a failed drive.

Many thanks in advance,

Tim