Backup your data from your Synology to the datacenter with daDup and Hyperbackup
Use Archiware P5 to make back-ups to daDup S3 storage. Safe in the datecenter to an external location.
ZFS is pretty memory hungry. There are circumstances in which you want to limit the amount of memory ZFS is allowed to use.
The efficiency of your Proxmox environment is immediately visible. The number of VPSs, the transfer of the CPUs and memory can be found in Insights for Proxmox.