

If you have new drives: make a zfs array and copy all files there
If you want to recycle drives while temporarily keeping the parity drives: from unraid 7 set a drive as unused, use the mover (or unbalance) to empty it, check if it’s actually empty by going to /mnt/diskX , format it as btrfs, set it as preferred for your shares, choose another disk to empty, use the mover to move all the data from the next disk to the new btrfs one, then remove the empty drive and add it to the btrfs raid. Repeat.
The unraid array it’s not an array, but a bunch of xfs partitions where a third party program is doing softraid. If opened on any other Linux distro, they will mount but parity drives are ignored