why can't I set power management to min power?

[sean darcy]

On F8 updated to today:

# echo min_power > /sys/class/scsi_host/host0/link_power_management_policy
# cat /sys/class/scsi_host/host0/link_power_management_policy
max_performance

Tried both on and off ac.

System > Preferences > System > Power Management doesn't set it.

I'd expect to be able to set it separately for battery and ac, but it 
seems I can't set it at all.

Any suggestions?

sean