There are two options for transfer presented by the Synology KB article

https://kb.synology.com/en-global/DSM/tutorial/How_to_back_up_Linux_computer_to_Synology_NAS

Of the two the first seems to be more glitchy and the -e ssh one I found tends to complete more reliably.

Also after the rysnc transfer locked up and I tried several time to get it going again I had to reboot the NAS to get it to start transferring again.

Also put --progress in as a paramater so you can see what's happening

# this one tends to error out with the following error more often
# rsync: [receiver] write error: Broken pipe (32)
rsync -av --progress home/ [email protected]::NetBackup/backupdata/

Copy from Linux to NAS

This command seems to be more reliable for rsync copies in both directions.

Not sure if this is because of firewalling between the two hosts but i find specifying -e ssh works more reliably.

# this one completes more reliably
rsync -av --progress -e ssh home/ [email protected]::NetBackup/backupdata/

Copy from NAS to Linux

rsync -av --progress -e ssh [email protected]::NetBackup/backupdata/ ./backupdata/