Possible bug somewhere down the line when it comes to the sleep state of usb drives.
 

On Slackware 13.37 it would spin down my external drive, and that was when it was mounted and not in use. Now on the current version of Slackware and fedora, my external drive will not spin down. This also happens when the disk is not mounted but still connected, when unconnected it spins down.

Any ideas, or commands to run with acpi or hdparm?

The command I used to get it to sleep was hdparm -S5 /dev/sdb

For some reason it won't spin down unless I do that.