Dear Ken--
I tried to follow your suggestions but they did not work for me. I fully control the server and I can see newly created folders in moodledata/temp/backup, I can also see a huge file for each course that I cannot back up there named backup.mbz (renamed it to fit the moodle convention for backup files and I tried several backup files). I can unzip this file successfully but I cannot restore it. It gives me:
error/tmp_backup_directory_not_found
I'm running Moodle 2.9.1 on Windows 2012R 64-bit server, PHP 5.6.16 32-bit, MySQL 5.7 64-bit. I have 16GB RAM and a lot of space on my hard drives.I have the same errors that David described for backup files bigger than 2Gb. The smaller backup files are fine. I cannot back up manually or automatically with or without CLI script.
I feel that I need to change settings somewhere to increase the allocation of memory beyond 2GB on the temp directory. But I don't know how to do that. I cannot find any setting in my php.ini or my.ini files. I've increased php processing time for several hours.
Any ideas? I'd appreciate your help.
Thanks,
Eugene