Sync between multiple locations - same file accessed in two locations

[michaelpop]

Hello,
Our company has three locations. Currently, all data is stored in the central nas and they connect through VPN. However, although they have a very good internet connection, some of them have very low VPN transfer speed. I suspect that this is due to a bottleneck between the locations, else I don´t have any explanation why only from that location and with a gigabit internet speed, the VPN transfer speed is 4-5mbps, while others from other locations who use VPN have transfers of 100-200mbps.
Therefore I thought of installing two more local NAS at the remote locations, to sync with the central one. For one question I didn´t find any answer, and it´s critical: What if one user from location A is opening file 1, after 2 minutes one user from location B is opening the same file 1, user from location A saves and closes the file and then later user from location B saves and closes the file? Is there any feature to lock files which are open on a synced nas? Or what would be the solution for such critical files?
Thanks in advance,
Michael

 

[Rusty]

Maybe this official article will help: Why is there file conflict on Synology Drive and what can I do? - Synology Knowledge Center

 

[fredbert]

Does the ISP at the problematic site apply QoS and packet shaping, or maybe you have this in your intranet/perimeter infrastructure? I'm assuming you are using site-to-site VPN with concentrators terminating each end, not user-to-LAN/site remote access.

Or there may be traffic control rules on the NAS?