the command you suggested will have written zeros to the entire disc, but does that take damaged areas out of service?
The disk firmware should re-map dodgy sectors during write to a spare sector, seamlessly from a user point of view, and adjusting the relevant attribute counts in the SMART data.
Is the point that it's a sufficiently modern drive to have smart features, and does this automatically during the dd process.
Yes. Writing to every sector on the disk should re-map all that are unreliable, until it runs out of spares.
a few results seem to be recommending using other commands, like badblocks and fsck.
fsck just fixes the filesystem - it doesn't nothing to the physical disk surface unless a write happens to coincide with a bad sector, in which case the above applies.
badblocks, with the appropriate option(s), can be useful for non-destructive (as far as possible) testing.
To have the disc in the best condition going forward should I have run additional commands?
Not really. I'd have expected it either to have been fixed properly or to have told you that it couldn't (by the counts remaining non-zero) but it seems to be in some half state that I've never seen. You could try running
badblocks on it and/or another long SMART test to see what happens.
The Humax itself, when presented with the wiped drive, asked me if I wanted to reformat it and it was almost instantaneous. I'm guessing all it did was create the basic filesystem, and not do anything at the low level...
Absolutely. Creating a filesystem is all it's ever going to do. It does not do anything to fix the disk sectors unless one of its writes coincdes with a bad sector, as for
fsck and
dd.
Bear in mind also that sometimes the faults on the disk are beyond what SMART reporting can seemingly cope with. Your choice then is to carry on with it, accepting this, or replace it with a new one. It depends what value you put on the data and whether you have backups etc.