If I understand correctly, you have a server that provides services and now you want a second one for backup or failover?
I would try to use ZFS on both systems. This would give the best possible datasecurity, Ransomware secure versioning with read only snaps and ZFS replication. This is a high performance method to keep two servers in sync even with open files, even on a high load Petabyte system down to a minute delay between. No other sync solution can offer this.
The best ZFS OS is Oracle Solaris Unix (where ZFS comes from) with genuine ZFS v44. Next best are the free Solaris forks with Open-ZFS. All of them are full featured server OSs with services like NFS, SMB, iSCSI, network virtualisation as genuine Solarish services (no third party software like SAMBA or others) needed. ZFS is the only supported filesystem on Solarish with best of all ZFS integration.
Next best are solutions based on Free-BSD Unix where Open-ZFS is implemented for a long time with similar services like on Linux but a strong focus on ZFS.
Open-ZFS is also available on Linux but lacks the integration quality of Solarish or Free-BSD. If your main system is Linux you would need to check if you can use ZFS and ZFS replication. The replication should be possible between all Open-ZFS platforms (not with genuine Solaris ZFS)