Debugging for manual backups to see that process is running correctly. Obviously, that won't help with automatted backups. However, there is commandline script called automated_backups.php in admin/cli/. Handy for troubleshooting auto backups and forcing it to run (errors would display there).
Apache on Linux can write to directories outside document root and apache root if those have proper ownership/permissions set without having to create aliases/etc. in the apache config. Have heard that IIS might require some config additions for that to work, thus the suggestion concerning the other directory for auto backups.
Also, the entire process requires temporary files/folders be created, copied, and then removed. Moodle has a temp, php has a temp, and, of course the OS has a temp. When ever I have issues with backups/auto backups I check them all ... especially the moodledata/temp/backup folder/directory.
Can't remember which PHP version, but on Windows systems it had an issue with being able to 'unlink' a temporary file/folder, thus could not delete. Those types of errors would show in apache error logs. IIS logs? (dunno).
Inspecting the tables for Moodle, there is one for backups (controller) that uses UNIX epoch time and could see if the system/operating system or php time is not sync'd or correct or functioning, that might affect the cron'd and auto backup routines.
Sill trying to understand how that table is used. :|
'spirit of sharing', Ken