HDD shutdown after a random time.

[onetx]

Software
XBian version: 1.0Beta1.1
XBMC version: XBMC 12.2 Git:20130502-32b1a5e
Overclock settings: Xbian

Hardware
Power supply rating: 2 USB Power supply both with 5V/1000mA.
RPi model (model A/B 256mb/512mb): Model A 256mb
SD card size and make/type: 4GB Kingston
Network (wireless or LAN): LAN connected and Wireles TP-LINK TL-WN725N
Connected devices (TV, USB, network storage, etc.): HDD Samsung External Drive 500GB

Logile
Link to logfile(s):
usbmont.conf http://paste.debian.net/58940/
dmesg | tail -90 http://paste.debian.net/58944/
fstab http://paste.debian.net/58945/

Problem description:
I’m not a LINUX expert so I spent some time trying to setup a torrent client with my Raspberry Pi. I have already reached it with Transmission Daemon but I have a problem now .

I use an external HDD powered with a Y USB cable (like this: http://ww2.justanswer.com/uploads/space143/2011-06-07_001706_cable1.gif) connected to a power supply (1A) and to Rpi. And another power supply (1A) to the Rpi.
I connect to Rpi with SSH console because I don't connect it to a TV.

Transmissión torrent software runs correctly. If I do a "df -h" I see the drive mounted in "/media/HDD LABEL + UID folder". But HDD turn off after a time (60 minutes aprox). And I should reconnect the USB HDD to Rpi and login into Transmission Remote to reinitialize the dowloading process.

How to reproduce:
See before.


Thanks a lot!