1,236 Speed Tests Expose 4AM Backup Slowdowns, Burning 2.42TB in 104 Days

Q: Why did a homelab user's gigabit internet mysteriously crash every night at 4 a.m. for weeks?

His gigabit internet was not crashing because of his ISP at all; it was being saturated by his own overnight cloud backups. The homelab user ran automated speed tests every two hours for 104 days and found a repeatable slowdown starting around 4 a.m. from late April into mid-June. During that window, download speeds fell sharply from near-gigabit levels to about 152 Mb/s, while upload speeds also dropped. The timing matched a backup routine he had started after a major data-loss event. He was sending large amounts of data to the cloud in small batches between roughly 3 a.m. and 6 a.m. Those transfers consumed substantial bandwidth, especially upload capacity, and that congestion distorted the speed-test results. This fits a common networking pattern: scheduled backups and other heavy background transfers can bottleneck a home network even when the broadband line itself is healthy. The evidence was clear when the backup jobs stopped. Speed-test results returned to normal, with the connection again averaging close to the 940/940 Mb/s service he paid for and uploads even peaking above 1 Gb/s. That showed the slowdown was internal, not a provider fault. The broader lesson is that repeated, wired speed testing can reveal whether a problem comes from the ISP or from activity inside the home. In his case, testing every two hours was enough to expose the pattern without excessive waste, though it still used significant data.

1 articles · Updated · How-To Geek · Jul 30

1,236 tests run over 104 days showed a repeat slowdown starting at 4 a.m., when download speeds fell from an average 930.8 Mb/s to 152 Mb/s and uploads to 455 Mb/s.
A major homelab data-loss event at the end of April triggered cloud backups from 3 a.m. to 6 a.m., and the slowdown disappeared after those large transfers stopped in mid-June.
2.42 TB of test traffic was consumed at a schedule of 12 checks a day—about 24 GB daily or 720 GB monthly—making more frequent testing hard to justify for capped plans.
Historical tracking, the author argues, is most useful for spotting recurring ISP throttling or proof that paid-for 1 Gb/s service is only delivered at certain hours.