Two 4TB servers, two locations, best way to sync live data via internet

My work has an office in two locations (Dublin and Cork).

We have a 4TB Network Server in both locations containing the exact same data.

We currently use software by Globalscape that basically manages the syncing of the two servers in realtime - the software uploads new or edited data from Dublin to Cork, and vice versa.

The software also manages access to the data, so it is aware if a file is already open in Dublin or Cork, resulting in read-only access in the alternative location (just like in a normal server situation).

The software has many other capabilities (such as keeping shadow copies etc.) but the basis of the software is that it keeps data on two servers in two locations synced in realtime.

Please note that there is no cloud data involved in this synchronization data.

Unfortunately this software has recently burned us during an upgrade of the software whereby data become corrupted / lost and we are now seeking alternative software solutions. It has involved significant downtime for the office and we are still trying piece back together the information.

I was hoping someone on Boards might be able to advise of a similar software solution that we could replace Globalscape with.

Initial research would suggest sugersync would be perfect for our needs but cost for anything over 1TB is significant (they are approximately €2000 per TB).

Any assistance or recommendations would be much appreciated.