Btrfs seems to have a set of useful features such us snapshots and is default in Opensuse and Suse.Fedora plans to move to it. Does Ubuntu plan to move to it? If not, why ?
I'm not sure when, or even if, Debian or Ubuntu will switch to Btrfs as the default root filesystem. Seeing as how it's just recently "become stable" I wouldn't be surprised if it were years before it reached Debian Stable (but Ubuntu's based on Debian Unstable...). If it were me, I'd wait and see how it goes for openSUSE for a while.
It seems that "snapshot and rollback [is] the killer function of Btrfs" mentioned in this openSUSE news page, but it sounds like a solid backup strategy that you can implement in any FS today with a little effort. I do like the compression feature, I think it uses ZLIB now, but I don't think it would compare to something like what
xz uses by default.
This guy on LinuxBSDos.com says "With Btrfs the default on openSUSE, when will other distros follow suit," but says that while a default install uses Btrfs on root, that " a separate partition for /home, uses XFS." Then adds "One thing that caught my attention in openSUSE 13.2 is that the root partition cannot be encrypted, with Btrfs selected. I think that’s because in the default partitioning scheme, there’s no separate partition for /boot."
A comment makes the educated guess that "Btrfs is on root because in case of unexpected troubles, you can always re-install the system. While on /home where there are user data, you can not count on a re-install."
I actually didn't know Btrfs was stable, just read that it became "stable" sometime around August 2014 - if Wikipedia qualifies as a good source (Ubuntu's Community Help Wiki on Btrfs says Wikipedia is a "more info" link on Btrfs...), the link to the Btrfs Wiki says it's "no longer unstable," and still has:
The Btrfs code base is under heavy development. Every effort is being made to keep it stable and fast. Due to the fast development speed, the state of development of the filesystem improves noticeably with every new Linux version, so it's recommended to run the most modern kernel possible.
Actually the Btrfs Wiki's FAQ doesn't appear to have news about it's stability newer than Dec 2012 about either (I'm sure updating documentation is low on the priorities, but hitting stable seems like a milestone to me):
Is btrfs stable?
Short answer: No, it's still considered experimental.
Long answer: Nobody is going to magically stick a label on the btrfs code and say "yes, this is now stable and bug-free". Different people have different concepts of stability: a home user who wants to keep their ripped CDs on it will have a different requirement for stability than a large financial institution running their trading system on it. If you are concerned about stability in commercial production use, you should test btrfs on a testbed system under production workloads to see if it will do what you want of it. In any case, you should join the mailing list (and hang out in IRC) and read through problem reports and follow them to their conclusion to give yourself a good idea of the types of issues that come up, and the degree to which they can be dealt with. Whatever you do, we recommend keeping good, tested, off-system (and off-site) backups.
Pragmatic answer: (2012-12-19) Many of the developers and testers run btrfs as their primary filesystem for day-to-day usage, or with various forms of "real" data. With reliable hardware and up-to-date kernels, we see very few unrecoverable problems showing up. As always, keep backups, test them, and be prepared to use them.
The Fedora Project Wiki about Btrfs in it's "Btrfs filesystem DRAFT" says "As of Fedora 16 it is slated to be the default filesystem," but that was released back in 2011, so I think that page is useless...
The Red Hat Enterprise Linux 7 Storage Administration Guide calls Btrfs a "Technology Preview" and that RedHat version was released 10 June 2014 (with "End of Production 1 Phase" of Q4 2019).
In Red Hat, What does a "Technology Preview" feature mean?
Technology Preview features are currently unsupported, may not be functionally complete, and are not suitable for deployment in production. However, these features are provided to the customer as a courtesy and the primary goal is for the feature to gain wider exposure with the goal of full support in the future.