Getting "Input/output error"s! ReadyNAS doesn't care.

"Disk" io errors will likely show up against the disk device. dm complaining without seeing those disk device errors may just mean that the data is bad on disk. dm is a logical device that sort of lets you logically organize partitions. For example, if you suddenly lost power on a system, an extended attribute page could get "corrupted" and you'd see what you are seeing. The disk in that case could be fine. This is why the first person asked if you were having clean shutdowns. It's possible there was a real disk IO error earlier in the log or something that cause the corruption too. Which is why no one ruled out bad disk.

Can you show what the system log contained from the timeframe when you did the ls? There should have been an error logged then.

steve