What would you use to do a surface scan? (Why not just zero out and let bad blocks be written out?)
An HDD may come from the factory with bad blocks, which is not a disaster, but its developing
new ones during the course of its use is a
"sit up and take notice" danger sign*.
Therefore, my approach to drives is to run a surface scan immediately upon acquiring them (I'd follow up the discovery of any factory-issue bad blocks with a zero run, but I've never found any.), and to follow it up with subsequent scans, although on no particular schedule, to see if any new bad blocks have developed.
I suspect that you've never run scans on your drives, so you won't know whether any bad blocks you may find are factory-issue or newly developed, but knowing that they're there and zeroing them will give you both a fresh start
and the knowledge that you ought to keep close tabs on the affected drive.
You can run a surface scan from within OS X via Terminal (I'll walk you through it if you'd like.), but there are any number of 3rd party utilities that can do the job more easily. TechTool Deluxe, which shipped with all Macs at one time, is a likely candidate if it will run on your current deuced Mac(hina), but TechTool Pro and others of its ilk (but not DiskWarrior) can also do the job.
Edit: * See
this post by joemikeb.
