How to storage buckup of aspect server in external hard drive
In some but not all revisions, backup to a network drive has been possible.
I recommend first backing up to a local partition (rather not C:\) and later compress and move the backup out of the server with some script or PowerShell. The script should react on the result code in the backup log, eg don't purge the last known good backup before a new exist. If backup run at 0300 the compress&move script could be scheduled at 0400, 0500, etc when the backup should be ready (again, script should check log for backup's validity and completeness)
Backup Service Provider Definition Aspect
It is possible to make specific configurations of the Backup Service Provider object. Select the object in the Service Structure. Go to the Service Provider Definition aspect and select the Special Configuration tab. See the figure below.
In the Path definition area a root directory (Backup Path) for all backups can be set. It is made by the Backup Service provider. The default value for the path is set in the Storage Path area under the Configuration tab of the Service Definition aspect.