Recently completed my first unraid setup using a few random 500gb/1tb hard drives I had lying around.  After using it for few weeks, I am thoroughly enjoying it and I think it may be worth it to upgrade to a few high capacity NAS drives.  Just wanted a quick sanity check on what I'm planning to do and make sure its the correct process. 

 

So I am looking at getting 2 4tb HDs (HGST or WD Reds) for now.  One will replace the 1tb parity drive and the other will replace a 500gb drive.  From what I've read, I should use the preclear plugin to preclear both these new drives before adding them.  Once they are precleared, I should replace the 1tb parity first and let it rebuild.  Second, I would replace the 500gb data drive and let it rebuild it as well. 

 

Since the drives are to be precleared before swapping will this lead to minimal downtime of the array or will it still take a while to rebuild?  Is this the correct order of replacing with new drives or is there a better process?

 

Thanks!

You've got it right.

 

It will take a while for each rebuild, but your server is not really down during a rebuild. You can still read and even write to your server while a rebuild is going on. Rebuild and other I/O will compete for disk access of course so there will be some performance impact.