During backup the SMS Writer service is used. This is a service that interacts with the Volume Shadow Copy Service (VSS) during the backup process. The SMS Writer service must be running for the Configuration Manager site back up to successfully complete. Just make sure that this service is running!
When creating a Maintenance plan in ConfigMgr there is a choice for Destination options. When selecting "Network path (UNC name) for site data and database" a UNC path is needed where both ConfigMgr data and SQL data is saved. Just create one folder, place a (hidden) share on it, and data will be saved. When selecting "Local drives on site server and SQL server" a local drive on both ConfigMgr and SQL server is needed for backup. Backup data for ConfigMgr will be saved on the local drive specified on the ConfigMgr server. Backup data for SQL will be saved on the local drive on the SQL server.
Microsoft recommends as a best practice, to keep multiple archives of the backup snapshot. You can create the AfterBackup.bat file to perform post-backup actions automatically after the backup maintenance task runs successfully. The AfterBackup.bat file is most frequently used to archive the backup snapshot to a secure location. However, you can also use the AfterBackup.bat file to copy files to your backup folder and start other supplemental backup tasks.
Additional information on Backup Site Server task can be found HERE. Hope it helps!