by Ken Task.
Pardon jumping in here ...
Think this is key/clue:
Exception: storedfilecannotcreatefile
Status 800 is short of 900 and 1000 - 1000 normally reached when backup is successful.
Check apache error logs ... do you see a 'Server has gone away' error?
If so that's due to max_packets_allowed setting too low (default is 16M).
Refer:
https://dev.mysql.com/doc/refman/5.7/en/program-variables.html
Add a line to my.cnf under [mysqld] section of config file:
max_allowed_packet=32MThe other to check, since you've said it's a large course, is the settings in php for time for a script to run. Default is normally 30 might want to increase that to 60 or 90. Restart apache.
Also check moodledata/temp/backup/ for any files/folders left over from failed backups. Can manually remove the contents of moodledata/temp/backup/ with no ill affects.
There is a clean up task to check as well - which is supposed to execute when cron job is run to clear out that temp area. Running automated backups that task needs to complete successfully or one could 'run out of space' (eventually).
That to say .... cron job needs to run frequently.
All the above 'educated guesses' having had deal with a site that had 1 130+ Gig course when backed up and autobackups could never really finish.
'spirit of sharing', Ken