“A couple of days ago, I had a 518GiB tar.gz file (1.1 TiB uncompressed) that I had to extract.”
Extraction started at 100MiB per second and fell below a kilobyte per second. GNU tar rescans its list of delayed hard links for every new hard link, which makes the whole job quadratic. The fix is a flag that trusts the archive. The most common archive tool on Unix falls over on big data, and nobody noticed for decades.