Error after freebsd-update

I have just applied an update to FreeBSD using the freebsd-update command to update from 10.1 to 10.2. The update went smoothly, but after a reboot, whilst running:-

/usr/sbin/freebsd-update install

as per instructions here

I get this msg

smartd[769]: Device: /dev/ada0, 1 Currently unreadable (pending) sectors

Any idea what I should do about it? How do I find this unreadable sector?

I'm not aware of any related problems at the moment.
That is an indication your disk has bad sectors and will need to be replaced.
Don't do that. Modern disks have a "spare" bit of the disk that's normally not accessible. The drive's firmware automatically maps bad sectors to this bit of spare space. The fact that bad sectors are showing up means this spare bit of space is now full and bad sectors cannot be mapped anymore.

Replace the disk.

Edit: Due to a misunderstanding getopt removed his post. It referred to There's a lot of good information there.\
My "don't do that" refers to mapping or otherwise excluding the bad sectors. That's a bad idea on modern harddrives due to the "automagic" mapping the firmware already does. Once bad sectors start showing up there's really no other course of action than replacing the disk. This is covered by the drive's warranty and shouldn't pose an issue.