BTRFS Quirks
- Since BTRFS filesystem uses copy-on write meaning that it writes changes of data in free blocks rather than overwrites the original data, files can be fragmented.
- In 2015 BTRFS is still "young" filesystem and have not been yet tested on a wide base of users (as compared to NTFS or ext-series filesystems).
More than that, new features are still added meaning that one should not expect more or less stable version of BTRFS in the coming year.
You may take a look at the current list of open issues yourself.