I run double parity, also. It's 1/2 for peace of mind and 1/2 because I'm a nerd and multiple parity is seriously cool stuff.
Worked great! I've simulated a few scenarios in the past by moving files to another disk, but this was the first time I needed it.
I couldn't leave well enough alone, though, and finally found a solution that works Even with write-protected folders.
From an administrator-level command prompt type: "Robocopy C:\Test C:\Test /B /S /Move"
I don't understand exactly why it works, but you're basically moving a folder onto itself, but skipping (deleting) empty folders.
/B allows Robocopy to properly set attributes and permissions for system folders like Recycle Bin and .covefs. Bad stuff happens if you don't use it.
I wrote a batch to run this script on all 7 of my Drivepool disks, and it completes in under a minute. Good stuff.