Adding the first parity disk

[kasperfm]

Hi

I have an existing data array, made of 3x 3TB WD Red disks.

I then found another 3TB WD Red disk, and want to add it as a parity disk, as I didn't have one before.

 

Now my problem is when I add the extra disk as parity drive, I can't start my array because of the message:

If this is a new array, move the largest disk into the parity slot. 
If you are adding a new disk or replacing a disabled disk, try Parity-Swap.

 

Maybe I don't get the parity thing right, but how can I fix this?

[RobJ]

Sounds like you added a 3TB Red that's a bit smaller than the others.  That happens sometimes when you pull one from a USB drive shell.  They should be the same size, but often aren't.  Drives like that work fine as data drives, because the size difference is minimal, but they can't be used as parity drives, which HAVE to be as large or larger.

 

You can either buy another drive that's large enough, or you'll have to do the Parity-Swap, see The parity swap procedure.