Matt Simmons, the Standalone Sysadmin comments:

Yesterday, I was reading a thread that asked about failure scenarios involving RAID-5, and like all discussions related to RAID-5, it was full of misinformation stemming from misunderstanding.

A lot of the comments seemed to think that because Unrecoverable Read Errors (UREs) were presented as probabilities across bits read, that having previously read a certain number of bits increased your chances of encountering a URE while rebuilding a drive. I meant to reply to explain what a URE is, and give an example of something that would cause a URE, and ended up writing a novel.

Read more at: Hard drives and UREs (or “What’s really going on?”)