Hard disk keeps turning off or disconnecting?

[Gilles Gravier]

Hi!

I have a strange problem. Ubuntu 12.04. All latest updates and kernel. I
used to have a 2TB disk connected by USB 2.0 port. I replaced this disk
(a Western Digital) with a 3TB (same brand, connected on same USB port).
Now, every 3 or 4 days, suddenly, the disk gets disconnected. As if it
wasn't mounted anymore. Didn't have the problem with the 2TB.

But... I seem to recall having had that a long time ago on another
disk... and that this was due to some power management mode on the
disk... that had to be turned off...

Does that ring a bell to anybody on this list? Any magical command to
tell the machine to tell the disk that this is a server and I don't want
spin-downs?

Luckily, this is an ext4 volume... so I don't lose any data. I just have
to turn off the machine, turn off the disk, then turn everything back
on... But this is clearly sub-optimal. I would like the machine to keep
running...

Thanks in advance,
Gilles