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>> okay.  What's the recommended action at this point?     -- George
>
> In my experience it is begin of disk death, even if overall status is
> PASSED. It could work for month or may be half a year after first
> Offline_Uncorrectable is detected (it depends on load), but you best bet
> to replace it ASAP and throw away.
well my disk had this and live happily for 3 years.

It JUST means that some sectors are unreadable which may be a reason that 
at some some write got wrong because of hardware problem. But this problem 
may be - and possibly were - powerdown while writing, or power spike.

the media itself could be fine. the best action in such case is to force 
rewrite whole drive with some data.

with gmirror it is as easy as first checking second drive for no errors, 
then forcing remirror.