It’s important that before you start you understand the concept of volumes on Synology Diskstations, because that’s the first thing you will need to set up before you set up Time Machine backups.
Volumes on the Synology Diskstation
You can use the Synology RAID calculator to help determine how you want to set up volumes. That being said, in this case you want to just make one, and then create shares to logically organize things.
The advantage to creating multiple volumes comes when you are using different size drives, want different levels of redundancy, or have significantly different uses .Let’s take an example a NAS with 4 x 6TBb drives. The only advantage you would gain would be less loss of data if an array fails, but at the cost of a higher risk of array failure.