Backblaze Synology Backup
Backup providers who offer 'unlimited' items don't want you to back up your NAS to their service, since it's really designed to let normal people backup their everyday files vs. A pro or enthusiast-level of data. B2 is a great deal for backup though, especially now with Arq support. First, log into your Synology and open up Package Center. Download and install the CloudSync Application. Next open Cloud Sync and Click the + sign to add a vendor. As you can see there is a ton of vendors to choose from. We are going to pick BackBlaze B2 and click Next to continue.
It depends on the volume of data. Running a second Synology unit at another site and mirroring changes (using something approaching the efficiency of rsync) will easily be the most economical beyond 1tb -- an amount typically included for free with just about every Office 365 subscription. It's not ideal however, unless you plan to perform DR to the cloud; that is, restore a failed local instance to a cloud platform. This is because you will be unable to get one tenth of 1tb of data that stored in the cloud in a timely fashion unless it is being restored to an adjacent platform.
Backup Nas To Backblaze
The cool thing about rsync is that the bandwidth use can be near zero as you can do a full mirror once a week but generate a differential file each night and export it to a local drive instead of applying the changes over the internet. That differential file can be used to roll the remote version forward to the time the file was generated. You would only actually apply it to the remote mirror if need be -- testing notwithstanding.