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

First if it is working now, take a good backup. Best bet is to open a case with Netgear.

But, if you are out of warranty and still reading...

I don't see anything obvious. I'd run tests on the drives using vendor software and system memory using the nas boot tests in particular. Remember to make note which slot each drive came from. This drive test will also get the drives reseated which is good. Also this might be a good time to check and update the firmware on them.

A couple of the entries are interesting. The error on ext4_lookup that says "deleted inode referenced" means it actually walked a stale inode. That's different than garbage. It could be the code just ignored an error and processed some stale memory, but do you happen to have disk write caching enabled in the nas performance settings? If so, try turning that off for a while and see if you get more obvious in band errors. Deferred write errors are ignored by Linux (at least on the scsi stack that I'm familiar with). In theory software raid could help repair them but it's not even notified. Also almost every drive vendor has fixed firmware bugs in the area of disk write caching over the last couple of years.

steve