I wanted to upgrade one of my 1TB drives to a 6TB drive, but I need to find a way to pre-clear the 6TB drive prior to the swap.  My problem is that my server is completely out of SATA ports.  I was thinking of moving all the data off the 1TB due for replacement, but I don't have enough space on the array to offload the data to another drive.

A replaced drive doesn't need to be precleared, if you want to burn it in just use a different computer and the manufacturer tools or any other disk low level testing tool.

That sounds easy enough.   Just out of curiosity, Is there a reason that it's recommended to preclear a new drive but not a replacement drive?  

You have to clear (not preclear) a new drive to maintain parity, preclear was always optional, and used mostly for disk burn in or to preclear the disk before v6.2 to avoid the array being inaccessible during the clear, since v6.2 a new disk is cleared in the background with the array accessible.

So I swapped in the new drive using then wiki article I found on upgrading a drive. 

 

My log is now filled with these errors:

 

Jan 18 17:47:32 Tower root: error: /plugins/preclear.disk/Preclear.php: wrong csrf_token

https://lime-technology.com/forums/topic/46802-faq-for-unraid-v6/?do=findComment&comment=545988