inotify is a file change notification system in the Linux kernel, and SpiderOak ONE and Groups on Linux rely upon it to watch your selected directories for changes. Each watched directory takes a small amount of memory, and because the operating system needs to manage memory use, it will automatically assign to SpiderOak (and every application that uses inotify) a limit to the amount of memory that is allowed to use. In practice this limits the number of directories (including subdirectories) which can be monitored.
When ONE and Groups are used as designed to back up user files, the inotify limits are not hit and there are no problems. If you're trying to back up more directories than inotify allows, directory watching and backup will fail. You may see in the application logs entries such as:
AssertionError: fs notifier exited 3 times, exit status 2: text: 'inotify_add_watch /home/user/.config/subdir/subsubdir/ 28 No space left on device\n'
Although Linux provides a way to change the inotify limit, this problem almost always indicates that ONE or Groups is monitoring files that it is not designed to be pointed at. Our backup products are intended to back up user files, not system or application data, or code repositories. Our design works well for the intended use, but any rsync-like tool that runs in userspace would be a bad choice to back up system data. For more information on what to back up using SpiderOak, see What Data to Select for Backup.
If your intention is to perform a system backup, see System Backup.