My motherboard can support 6 HD and now all used: 4*2T SATA with 2*SSD Cache Disks. Due to some reason, I did not setup parity disk, now I got 2*4T HDs and I plan to replace one old 2T disk and add one as parity disk. Current my unraid OS is 6.9.1 and all data across Data array (8T) is 3.2T. As I have no additional HD port, how do I proceed since I have not configured parity disk before?

1. plugin one new HD with USB connection

2. Use "unBalance" to backup 3.2T data to the new one

3. Stop Array and replace with 2 new 4T HD and then go to Tools-new config

4. Config Parity disk and new array, then restore data 

 

If it were me, I'd proceed a little differently. Since all your data will fit on one of the new 4TB drives, I'd temporarily connect one of the 4TB to another PC on the network, not the Unraid machine, and make a full backup of all your files before you touch anything in the Unraid box. Then, once you have a backup...

Use unbalance to move data off of your 2 worst data slots, either oldest drives or any showing errors, so you have 2 2TB with data and 2 empty.

Set a new config, assign the other new 4TB as parity, and the 2 2TB drives with your data still on them as data1 and data2. Remove the 2 empty drives.

 

Now, you have a choice, either stay protected with a full backup, or erase your backup and replace one of the 2TB data drives with the 2nd 4TB drive that currently has a full backup of your files. If you choose to erase your backup, then you can keep the 2TB you replaced as a backup of those files, copy the other 2TB to the newly replaced 4TB data drive (not move with unbalance, copy) then do a new config with only the 4TB parity and 4TB data. Ideally you could get another 4TB and replace the 2TB, that way you would have more room to grow.

 

There is no scenario where I would recommend using a USB connection with Unraid, gigabit ethernet is more reliable in my opinion.