A couple of days ago I started getting these errors whenever I ran anything that scanned for logical volumes (Linux LVM2):
Buffer I/O error on device dm-6, logical block 0
Buffer I/O error on device dm-7, logical block 0
Buffer I/O error on device dm-8, logical block 0
Buffer I/O error on device dm-9, logical block 0
My first reaction was panic, as I initially believed my HDD was failing, but after some investigation I realised that the above devices simply didn't exist.
Apparently there is some problem with the Intel HD Audio kernel module in Linux (pretty much all versions) that prevents people from fully shutting down their PCs. See this bug report here:
This may affect any system that uses the snd_hda_intel module (snd-hda-intel.ko), such as my Giga-Byte GA-8ANXP-D. You can shut down, but you can't power off. Presumably this module is not releasing its resources (interrupt?), or something along those lines.