I have gone through two drives, other had only ecc errors and the replacement also has sector errors. I did some digging and theory of what is going on:
Here's pretty good article that goes to explain HDD theory and error correction. Suggest seeing the part about System Area and Bad block tables.
http://www.myharddrivedied.com/presenta ... paper.html
My theory of this is that the HUTIL 2.10 is actually working perfectly besides the Check MC thing.
quotes from the article:
"When the drive is manufactured it is known that there is going to be errors in every drive. Drives use ECC to correct most errors and if ECC can correct the error then the sector is never marked as bad."
Why other tools do not show errors besides HUTIL? Most obvious explanation is that they use a higher level read (similar to reading from Windows) that can only tell errors of such magnitude that drive should be replaced (eg. unable to correct the read data and reallocate the bad sector). But of course there's varying degrees of success/errors since we are talking about analog device. Different manufacturer and command may expose different data, some of which is only meaningful for factory/recovery business.
Hutil likely uses a lower level read command that passes over every sector, even those already in the "P-LIST" as referenced in the linked article (scan: SECTOR ERROR). These sectors were marked as bad in the factory and won't be used by the OS but are not skipped by this low level read.
http://episteme.arstechnica.com/eve/for ... 9007293831
http://www.hydrogenaudio.org/forums/lof ... 50484.html
Depending on the hdd manufacturer, they may or may not expose the ecc data in SMART values for example (Maxtor, Samsung seem to do this). However all drives would use this prml+ecc method to get better data density so you see the values change fast in SMART if you read maxtor or samsung disks. Why does HUTIL show ecc error for only some sectors then? I believe there's some sectors that aren't quite broken but maybe take extra effort to read, this can be seen in HDTACH and other tools by looking the Tranfer rate, it's not very steady, there's lot of tiny drops. Still there's no audible seeks or huge drops which would happen if it was bad sector that would have to be read from other part of the disk. This doesn't happen with all drives though, depends on manufacturer mostly how steady their read speed are.
I believe HUTIL 2.1 is working better than other tools, you get low level information you can't get from other drives!
Which drive to RMA?
ECC/Undefined errors, these don't affect perf in a noticeable way in my testing and so no reports have been seen that data written in these areas would be lost.
Lot of SECTOR ERRORS? It seems that if you have sector errors, these areas are reallocated to outer edge of the disk or somewhere very near: On my disk Sector errors, the performance GOES UP when reading the part of the disk where the errors are (perf better at outer edge of the platter). However there is risk that the problematic area spreads to previously good sectors when used, seen this happen. So I would personally return a drive that has more than a few hundred of these. I have more than few hundred so I'll probably replace.
New HUTIL version? I believe they just change it to use higher level read so that drive turns up "ALL OK" up to the point when you lose data.
edit: Based on some perf tests, I think the Sector Error areas are factory reallocd with a large margin: eg. 500 KB of errors in position x: realloc: 500 KB + a whole lot around it. This would decrease chance of new data being near the bad sector area and would make most sense to lower risk of data near the bad area.