Can mirrors be updated more frequently like every 6 hours, The answer is, basically, no. For starters, we'd have to contact mirror admins and ask them to change. Not easy, or fun.
Second, we'd have to push ftp.gnu.org to ibiblio more often, and doing anything with that connection is such a headache that I don't want to go there. Third, even if all that happens, it is inevitable that some mirrors will be unwilling or unable to implement it. Fourth, even for those mirrors who do implement it, I doubt six hours would be fast enough for you guys. I don't get the impression anything but up-to-the-minute replication would be fast enough, and that's not going to happen. or avoid in some way to redirect to a mirror that wasn't updated after the requested file mtime? Technically, it's possible, since anything's possible. But the current redirection mechanism won't do it and I doubt Randy wants to implement it. It's also not clear to me that it would really be the answer, or just get us in deeper. Imperfect net connections are a main source of problems, so the checks themselves could cause more trouble. I guess I didn't make it clear, but the expectation of ftpmirror.gnu.org was never that it would be perfectly up to the minute, or hour. The idea is that most people do not both (a) read an announcement and (b) dory the download within a few minutes of the announcement being sent. If the few people who do (like most of us on this list, probably) all go to ftp.gnu.org, that won't matter. Probably the most important thing for ftpmirror is to use it on the web pages, where people are downloading asynchronously from the announcement and ftpmirror will likely work fine. Sigh.