I don't want to change firmware if possible as the router I want to use this on is quite important to risk shutting down.

All I need is a hdparm binary compiled for BCM5365P/BCM5364P. Can you help?

It's a good idea to shutdown any USB hard drive connected since running one 24/7 will burn it out and waste electric.

Bear in mind that the USB adBRONET1apter you use will need to support the shutdown command - most do, but not all.

hdparm -y /dev/ ?

Code:
[admin@WL500G root]$ ls /dev/scsi/host0/bus0/target0/lun0/
disc   part1  part2  part3  part4
[admin@WL500G root]$ ls /dev/discs/
disc0
[admin@WL500G root]$ ls /dev/discs/disc0/
disc   part1  part2  part3  part4