As the title says, it is impossible to pause and resume the update once began. This is a major concern for large patches such as the most recent Stormblood expansion patch, since if there's even a small hiccough in the download or internet connection then the entire download has to be started over from the beginning.
This is completely out of touch with the current industry standard where downloads are able to be resumed whether paused intentionally or unintentionally due to an interruption.
Case in point: I have as yet been able to download the Stormblood patch due to this issue, since my current router does not like large downloads and stops connecting to the dns server after about a single download of around 500mb to 1gb depending on fickleness. While this router issue is on my end, the fact that the ffxiv launcher forces an all or nothing download greatly exacerbates the issue. If it had the ability to resume progress where it last left off like with every other major game and game delivery service I use then I would at least eventually be able to download the update in pieces. As it is, I'm stuck completely without the ability to complete doenloading it at all until I get the router issue sorted. (Which is not easy btw. It's exceedingly difficult to even get my isp to recognize there's an issue with the router since their solution is just to reset it which doesn't actually solve anything, and it's only complicated by the fact that the isp is provided via my landlord as part of my rent making it difficult to even communicate with my provider directly.)
P.S. If anyone knows of a torrentable version of the NA update that I can use to bypass the clunky official launcher mechanics please let me know. I don't want a pirated version of anything, just a way to get the files on my computer so that the official launcher can recognize that they're there and complete the patch.