First time I suspected that problem, I wrote a tiny program that scanned the disk for slow blocks then marked as bad each block and extra megabyte to prevent di

First time I suspected that problem, I wrote a tiny program that scanned the disk for slow blocks then marked as bad each block and extra megabyte to prevent disk's readahead from hitting bad blocks too. You are probably using a kernel filesystem, some of them let you provide a list of bad blocks to mark and avoid, I haven't tried that though.