We're strongly considering using something else until this gets addressed. The problem is, we don't know what, because every other CoW implementation also has issues.
* dm-thinp: Slow, wastes disk space
* OverlayFS: No SELinux support
* aufs: Not in mainline or CentOS kernel; rename(2) not implemented correctly; slow writes
Have you had any issues to report? If so, how quickly were they fixed? Knowing what the typical time is to address these issues would help us make a more educated decision.
Yes, we've run into 2 or 3 ZFS bugs that I can think of that were resolved in a timely fashion (released within a few weeks if I recall) by Canonical working with Debian and zfsonlinux maintainers (and subsequently fixed in both Ubuntu and Debian - and upstream zfsonlinux for ones that were not debian-packaging related). Of course your mileage may vary, and it depends on the severity of the issue. Being prepared to provide detailed reproduction and debug information, and testing proposed fixes, will greatly help - but that can be a serious time commitment on your side (for us, it's worth it). Hope that helps!
zfs is not in mainline or centos kernel, so you are presumably willing to try stuff. I believe all the overlay/selinux work is now upstream, it is supposed to ship in the next RHEL release.
https://github.com/zfsonlinux/zfs/issues/5535
We're strongly considering using something else until this gets addressed. The problem is, we don't know what, because every other CoW implementation also has issues.
* dm-thinp: Slow, wastes disk space
* OverlayFS: No SELinux support
* aufs: Not in mainline or CentOS kernel; rename(2) not implemented correctly; slow writes