I've downloaded the Torrent version of https://archive.org/details/stackexchange and selected only the files that I need with Transmission.
I then tried to extract with:
sudo apt-get install p7zip-full 7z x stackoverflow.com-Posts.7z
on Ubuntu 15.10 AMD64, 7z version 9.20, but it extracts up to 6.9 Gb of
Posts.xml, and then gives the error:
Extracting Posts.xml Data Error Sub items Errors: 1
and exit status 2.
I think this means the file is corrupted.
.7z I've tried extracted fine. This one is by far the largest, maybe the failure is related?