First, RHEL has deprecated support for the Btrfs file-system.
Btrfs file system
Development of B-tree file system (Btrfs) has been discontinued, and Btrfs is considered deprecated. Btrfs was previously provided as a Technology Preview, available on AMD64 and Intel 64 architectures.
Huh? Since when was Btrfs development discontinued? At least in the upstream space, it's still ongoing and Facebook (as well as other companies) continue pouring resources into stabilizing and advancing the capabilities of Btrfs, which is widely sought as a Linux alternative to ZFS. There's no signs of things stalling on the Btrfs mailing list. Especially as Red Hat hasn't been packaging ZFS for RHEL officially (but you can grab packages via ZFSOnLinux.org) as an alternative, this move doesn't make a lot of sense. While Btrfs development has dragged on for a while and short of OpenSUSE/SUSE hasn't seen it deployed by default by other tier-one Linux distributions, it's a bit odd that Red Hat seems to be tossing in the towel on Btrfs.
Red Hat's definition of "deprecated" in their RHEL context means (as shown on the same page), "Deprecated functionality continues to be supported until the end of life of Red Hat Enterprise Linux 6. Deprecated functionality will likely not be supported in future major releases of this product and is not recommended for new deployments."
Similarly in the Red Hat Enterprise Linux 6.8 notes, they confirmed they are also deprecating eCryptfs support:
eCryptfs file systemThe eCryptfs code is still maintained in the upstream Linux kernel and used by distributions like Ubuntu.
eCryptfs file system is no longer updated, and it is considered deprecated. eCryptfs was previously available as a Technology Preview.
These deprecated features of RHEL were pointed out to us by a Phoronix reader in the RedHat.com documentation. Let's hope they get clarified by Red Hat and turn out being specific to just RHEL6 and will not affect Btrfs in RHEL7 or future Enterprise Linux releases.
Update: I've now been able to confirm with Red Hat that this change affects RHEL6 only and that Btrfs will be supported in RHEL7, still bad wording in the documentation.