# July 22, 2013: making a 2.5" hard disk work in an external USB-powered box

I have two external USB-powered boxes:
• an Enermax “Jazz” with two USB connections: one for the power, the other for the data transfer.
• a LaCie MS25U3L S/N:13791107210254A with a USB3 connection.
I have two 2.5” hard drives:
• a Toshiba MQ01ABD075 (750GB). The current is indicated to be 1.0A under 5V (is this current a maximum or a nominal current?).
• a Samsung/Seagate Momentus ST1000LM024 HN-M101MBB (1TB). The current is 0.85A under 5V. It is a rather quiet hard disk.
Curiously, the Toshiba works in both boxes, but the Seagate works only in the Enermax box. I would expect the contrary, according to the greater power of the Toshiba (5W against 4.25W for the Samsung). Perhaps even more surprisingly, the Seagate one works correctly even if the power cable of the Enermax is not connected (we would expect a lot of needed power, because it does not work in the LaCie box).
Maybe it is not a problem of power, after all: this is confirmed after having removed and inserted again the Seagate into the LaCie box: now it works. I suspect that it is related to the narrow electrostatic strip on the box: maybe I connected the hard disk in such a way the strip was stuck into the port, making some kind of short-circuit (?).
Note that to avoid the classical problem of ever increasing cycles on the Seagate hard drive, it is sufficient to set “Advanced Power Management” to level 254:
$sudo hdparm -B 254 /dev/sdb /dev/sdb: setting Advanced Power Management level to 0xfe (254) APM_level = 254  Switching APM off by using a level of 255: $ sudo hdparm -B 255 /dev/sdb
/dev/sdb:
setting Advanced Power Management level to disabled
APM_level = off

does not work, in some minutes the counter Load_Cycle_Count increases. To make the setting permanent, uncomment the line “apm =” in /etc/hdparm.conf, and set it to 254:
[...]
#bus = on
# -B apm setting
apm = 254
# -B apm setting when on battery
#apm_battery = 127
[...]