Bad stick of RAM?

Could also be a bad IDE cable... but with the bad sectors always appearing near the end of the drive, it sounds more like a bad stick of RAM.

Good thoughts, cyclone3d, but I've tried two different computers and different cabling. Different memory between the systems, too. (I coincidentally also ran MemTest86+ for several hours on the one system and it didn't find any memory errors.)

berbil wrote on 2020-04-24, 17:49:

Then, I'll run WDDIAG, which will find the bad sectors and indicate that the "maximum number of reallocations has been exceeded." When I run ScanDisk, about half of the bad sectors are miraculously gone. [...] If redo the whole process from scratch, the overall statistics are the same, but the bad sectors are now in slightly different locations

See, if you have more bad sectors than can be relocated, restarting the whole process will always cause different bad sectors to be relocated, until it can't relocate anymore again. The remaining bad sectors may appear, disappear, and reappear again, because they are normally not completely dead, but unreliable. Scandisk unfortunately does several tries before marking a sector as bad, which is nonsense, because if a sector fails even only once, it should never ever be used again. Anyway, trash the hard disks, they are done.

Sadly an all too common problem with these old WD Caviar-series drives. I've a few of these with similar problems, where the bad sector size / location moves with every scan or reformat and if it's not that they suffer from the 'stiction' issue as well. I keep mine for nostalgia only but as @derSammler says, bin (or return).

I remember hearing or reading about computer viruses in the MS-DOS era that would mark the disk sectors in which they hid part of themselves as bad.

It might be an unlikely cause, but you might want to rule it out with a thorough scan, regardless.

Aw, too bad. Thanks for the input and ideas, everyone.

That makes sense about the sector reallocations hitting their limit with each new scan. I've read that old sectors can sometimes be coaxed back into working order if you can perform multiple read/write operations at the specific location on the disk, but I suspect it'd only be a temporary solution if the platter magnetization is degraded due to age or physical damage.

I tried the virus scan, too. Didn't find anything, but it was a good idea nonetheless.

I'm using the Caviar drives for a period-correct PC build, so I guess the unreliability is par for the course after all of these years. I went through a ton of these drives back in the day as storage capacities seemed to expand without limit. I don't think they were very good drives even at the time, but I have a lot of fond memories!

You can try getting a WD Caviar 6.4 GB or later. I'm using two of these 6.4 GB ones and they are very reliable, unlike the older ones. Not a single bad sector so far and they have a huge amount of power-on hours.

That's a good idea, derSammler. I just looked up a picture of those drives and I remember having a few of that newer style at one time. I suppose I could just create an 800 MB partition to match the mid-'90s vintage of the system I'm building. 😀