So I'm currently using Drivepool with SnapRAID for backup.  For SnapRAID to run quickly, I've turned off the regular balancers and instead just rely on file placement rules to keep everything in balance (I'm mostly just adding and rarely deleting).  I've started adding a couple of SSD drives that I'd like for everything to land on, then using a FIFO type policy move things to magnetic drives as the SSDs fill up.  What is the best way to accomplish this without the balancers shuffling around data