Oh, I see. You were remarking on edgan's use of the phrase "Ext4 does support".
So, firstly, both Red Hat and ext4 support FSs larger than 16TB. So, yeah.
Secondly, I mean, Ted Ts'o works for Google, rather than Red Hat, so it's not like Red Hat has any special insight into the inner workings of ext4. RHEL's lack of "support" for ext4 FSs large than a certain size wouldn't make me wary of using FSs larger than that size.
Ts'o & co. seem to be pretty careful, so I would expect that the worst that would happen would be performance issues.
Regarding Tso & co, I am not so optimistic. How they communicate on the mailing list is more like: "Look we wrote this, it runs on my laptop fine it might work for other workloads too".
There is no extensive test coverage run by against ext4 (at least I am not aware of it). This is not the first data loss bug in the ext4 codebase. Few years from now when enough users start to use it an get rid off these serious bugs from the code, I might even consider POCing it again.
I'm somewhat certain that -despite the name- xfstests [0] is the canonical filesystem test suite these days. (At least, I've heard the btrfs devs concerned about passing its tests and adding new tests in it to check corner cases in btrfs. I also remember hearing the ext4 devs mention xfstest.)
I read that mailing list tone as something more like "This software is offered without warranty and might shave your dog and weld your toilet seat down.". I mean, folks on the LKML talk in that manner about their patches, too.
Also, even XFS has had severe data loss bugs in the distant past [1] and much more recently. [2]
"EXT4 [on RHEL7] [Cerfified max FS size:] 50TB [Theoretical max FS size:] (1EB)"
Moreover, RedHat's lack of Enterprise Support for a configuration doesn't mean that that configuration is a bad idea, or is doomed to failure. :)