I refer to the question of mine file system that allow to specify different RAID level per directory and change it afterward. Should I ask about this specific problem here on meta? But then, the users who flagged the question might not notice my post and I would sure take a lot of combined time of unrelated readers.
Or should I flag the question for moderation?
First, your question is essentially a Shopping Question. Shopping Questions are Off-Topic on any of the Stack Exchange sites. See Q&A is hard, lets go Shopping for more details.
Second, what you're asking for is "Odd", to put it nicely. You'll spend an enormous amount of time administering the redundancy level of each directory. Your employer would be paying much more for your time (over the life of the system) than springing for an extra couple hard drives.
Also, English is probably not your first language, and it's somewhat apparently from the tone and style of your writing. It's not fair, but people may hold that against you when your question lacks business merit.
No, this is the right place to ask.
As one of the closers, my rationale (which I put into a comment that I guess got delete for being "snarky"... sigh ...) was that there was just too much wrong with the question for it to be a good fit for a Q&A site. Basically, any decent answer to that question would have to involve teaching you a book or two's worth of information on RAID and basic... uh, "disk stuff," at which point you'd realize why your idea is just... well awful, to the extent it actually even makes sense.
On top of that, it asks for a subjective opinion, without providing the information needed to get a factually based answer (what do you think would be the best setup?), which is the definition of a not constructive question in these parts.
Let me address this as one of those who voted to close the question, although I can't now recall which of the several possible reasons I used for that vote.
Quite apart from it being a shopping question, the very notion is extremely unprofessional in my opinion and leaving such a question open would only encourage other would-be administrators to ask similar questions.
Why is it unprofessional? Because it shows a complete lack of understanding of some of the more elementary principles involved. It also shows you have failed to do any real research on your own. Server Fault is for professionals and we expect a professional approach and attitude in the questions and answers.
