http://sn.1w6.org/file/mk-20140710T170635-9lwn5kl.html

@mk Also, I have one drive formatted as EXT4, and the other as NTFS (the idea was that I could then at least read one under Windows). But I suspect NTFS was what made things worse in this case - I've long had a feeling that when using NTFS with Linux it's not quite as stable as using a native filesystem - and if not that, it is at least slow. So, I'm now copying over the contents from the NTFS drive to one of the partitions of my 'repaired' drive, and when that's done I'm going to reformat it as EXT4 and then copy it all back. *sigh*