A missed backup happens when a scheduled backup does not start, usually because the backup scheduler was not running, or a configuration change was made on the client.
There are configuration parameters which specify what the MiBackup service should do with a file in use during a backup. For example, "Static" specifies that the file must not be modified during backup, and if the file changes during the backup attempt, it is not backed up. Platforms that do not support the Static option defaults to "Shrstatic" (e.g. DOS). "ShrStatic" specifies that the file must not be modified during backup. The MiBackup Service makes a three attempts, and if the file is modified during every backup attempt, the file is not backed up. "ShrDynamic" specifies that if the file changes during all backup attempts, The MiBackup Service should back up the file on the last attempt. "Dynamic" specifies that the first attempt to backup a file is accepted, regardless of any changes during the backup.
The MiBackup Service offers modules for special cases, e.g. Domino, Oracle, etc. which are provided at an additional charge.