A bit of scary story with happy ending. Below I describe how failing HDD may look in your syslogs, and how I "resolved" this issue.
NOTICE: when you see I/O errors anywhere, or you see something like this in syslog YOUR FIRST TASK IS TO MAKE BACKUPS AS FAST AS POSSIBLE!!! ONLY WHEN YOU ARE SURE YOUR DATA IS NOW BACKED UP AND SAFE, you may proceed with something like "fixing"!
Recently had an accident involving few bad blocks on HDD. The target was Seagate...