In the past, I would swap out the hard drive after receiving this message. Now, I'm running out of hard drives.
As the (other) Thomas already said, this is not (necessarily) an indicator of a hard disk error. It is most likely a soft error due to some other (logical) corruption of the hard disk, i.e. bad program, corruption of data in RAM prior writing them out to disk etc.
Unlike what Thomas said, it could *also* be the result of a hard disk sector loosing its contents, but this is rather untypical. Hard disks have (typically) several levels of error correction mechanisms, including checksums, and would under such circumstances rather return an unreadable block - if they don't replace it in first place by themselves.
After all this time, does our favorite OS offer a way to re-map the bad places on a drive and continue on? This partition is currently formatted with FFS.
Well, let's put it like this: Not in the sense you're expecting to.
If this is a SCSI disk, then those disks typically re-assign bad sectors themselves, unless this feature is turned off. So there is nothing to do. Aminet contains a utility (SCSIQuery) that lists the defect sectors of the disk. Don't be worried if this list looks rather long, this is normal. The drive keeps care of them, and it will replace them transparently to the filing system and the host computer.
If the disk runs really low on spare sectors, you can re-assign the sectors with SCSIFormat, (also on Aminet), which will low-level format the drive and will include (as an option) a media scan that will check for defective sectors and re-assign them. However, I really really recommend against it. It not only wipes the entire drive (not just a partition), it is also usually unnecessary, and in very rare cases, it might even render the disk unusable because some silly drive firmwares also erase their own firmware as part of the formatting process. So, you usually do not want to do that. (Unless you really, really know what you're doing!). So, specifically, not in this case.
Last but not least, while FFS does not allow to remap sectors, in principle one could pre-allocate bad sectors so they are not used for anything. But, as I already said above, this is usually handled by the drive firmware, so there is no need for doing that, and second, I am not even aware of a program which offers this as a service. So while a theoretical possibility, it is not practical at all.
In your specific case, I would not attempt to use DiskSalv. This program may do more harm. Rather, I would copy as many files from the defective partition as possible to another drive or another partition, run an FFS format on the defective partition, and then just copy all the files back. Aminet "SortCopy" can do that, for example.
This will bring back the partition to life, and to a correct structure. Reparing a life filesystem with DiskSalv is not recommendable, and it is not unlikely that it does more damage to the structure. Do not attempt this at home.
Greetings, Thomas