depends on what OS you are running, windows has Distributed File System Replication (DFSR) (https://msdn.microsoft.com/en-us/windows/desktop/bb540031#MainContent) where two servers sync each others shares and create a universal domain share that multiple users can access even if one server goes down. (two isn't the limit, you can have a lot, most enterprises have over 100 of them all around the world ensuring that their shares never go down)
this dude explains on how to install it on windows server 2016 (basically the same in 2012 R2)
ignore the VMware stuff, just follow the windows server stuff...
for popular Linux server distros such as Ubuntu server, DRBD does the exact same thing but with Linux hosts https://www.linbit.com/en/drbd-community/drbd-download/
