I have a question about it: can anyone tell how it deals with redundancy?
It seems to be distributed. If you are running Plan 9 on 3 machines, and one goes down, what happens to the rest of the system. Does it become unavailable?
Sure. It's been stated many times that Hacker News is for anything that might be interesting to hackers, not just "news" (anything that happened relatively recently.)
For those who are interested in Plan9, you may be interested in checking out the following:
* Plan9port (Plan 9 from User Space) ports a number of the Plan9 programs to Linux: http://swtch.com/plan9port/
* wmii (http://en.wikipedia.org/wiki/Wmii) is a tiling window manager that allows configuration through a Plan9-like filesystem. A number of people I know (myself included) were first introduced to the power of Plan 9 through wmii's extensive configurability.
* Go (the language) has borrowed a number of elements from Plan 9. One of the two main compilers (gc) traces its origin in the plan9 toolchain.
* Acme/Wily (the text editor). I'll have to confess that I never took to this much (as a Vim user), but give it a shot.