failing usb drive

[Andrew Henry <adhenry@bredband.net>]

I have a WD Mybook 320GB usb/firewire drive which is about 1 yr old. 
Warranty is 2 years I think.  It is fully encrypted with dmcrypt &
Luks.  I power it up once a day and it stays on for about 12 hours (as a
home server) and the manual recommends *not* turning it on more than
once a day.

Now it "failed" as in I ssh's to my home server and did ls -l on one of
the folders and several files came up red with question marks for the
owner group and file size.

I turned the server off and rebooted, and Luks failed to open the drive
and offered to drop me into a recovery terminal mode to fix the problem.

I didn't know what to do so I rebooted again and it mounted the drive as
expected.  It has been "ok" for 2 days now.

I have run smartctl -Hc /dev/sda and done an fsck -f /dev/sda and they
report no issues.  How else can I tell if my drive is failing??

--andrew