I have asked ftp.nluug.nl, a well-respected international mirror site that mirrors a significant portion of all open source projects out there, whether they would mirror download.openwrt.org, and they agreed, however, they wonder how to go about making this an "official" mirror, one that people know they can trust. Note that the actual Download link points to a page that makes absolutely no mention whatsoever of the existence of any mirrors. The documentation has a "Where to get Packages" page, which points to a wiki page listing two mirror sites, and which documents that using any mirror requires manual editing of multiple exact URLs in a text file. This is not a convenient mechanism to use mirrors.
Note that generally, for any open source project of any significance, having multiple redundant download locations is a basic part of the infrastructure of the project. I'm a bit surprised that OpenWRT seems to think that the solution to repeated outages of their one single download site is to "fix the hard disks".
Please, people, take the offer. There are respected sites out there that would be happy to provide a secure mirror of your download site, thus improving both availability and performance, but you will need to provide the infrastructure to make those mirrors an integral part of your software download procedure.
(Last edited by wfk on 9 Apr 2016, 17:06)