I got the message 'Bad block on disk 3' so I saved all the data (2 TB) except for about 10 files. Then I intended to mark the bad block(s) and continue using the disk for unimportant things.

HD Tune couldn't find a bad block, Chkdsk couldn't find a bad block and the file system had nothing wrong with it either.

The 10 files I couldn't get had the error 'Can't read from source' so I'm sure the bad blocks exist but that must mean that Chkdsk and HD Tune are not reliable. Is there a really good surface tester out there?

Thanks - rev