@trurl
No, each parity disk (1 or 2) must be at least as large as any single data disk. As mentioned parity is not a backup so why would you think it needed to be as large as the total capacity?
Yes, I understand its not a backup, I just wasn't sure if the Parity group needed to be equal to the total of the data array (and now that I type that out, it doesn't make sense in my head either).... Thanks for link, it clarified/reminded me of how parity works. I've forgotten that over the years...
I posted on another post about using rsync to back up data to en external drive for backup in case of loss. I'm currently doing that with a batch file on a windows server. Just running out of space there and evaluating other, growable, options instead of being locked down to a raid 5 array (which is what I have now).
@BRiT I'm planning to put an 8tb in as parity so I can slowly swap the 2tb drives in the data array out with 8tb drives.