Turns out that ext4 doesn't really support file systems of up to 24T because the robust set of tools for checking and resizing ext4 file systems doesn't yet support anything larger than 16T (the old ext3 limit). Oops!

Nonetheless, I have a huge man-crush on on Theodore Ts'o because I believe him to be the author of this snippet from the resize2fs man page:

Note: when kilobytes is used above, I mean real, power-of-2 kilobytes, (i.e., 1024 bytes), which some politically correct folks insist should be the stupid-sounding ``kibibytes''. The same holds true for megabytes, also sometimes known as ``mebibytes'', or gigabytes, as the amazingly silly ``gibibytes''. Makes you want to gibber, doesn't it?