You have an interesting problem. Can you give some background on the system you’re using?
What are the hardware specs of the Seafile server?
What OS and version of Seafile are you running?
Is the data store co-located with the Server OS or saved to an external volume?
Is the current backup being saved to a local volume or a network device?
When you say it’s difficult to complete a backup in a timely fashion, how much time it is taking?
Do you also need an off-site backup of the server (or the files)?