RHEL 7.x had taken lots of changes by default …
1.) Default file system changes: XFS
In RHEL7 /CentOS 7 and Oracle Linux have adopted XFS as their default file system.
Apart of these there are other numerous changes that you could find from faq forum like http://simplylinuxfaq.blogspot.in/p/major-difference-between-rhel-7-and-6.html
Some of them i found to be mandatory change before use it for Database Server in Production.
2.) Default HugePages is On On
Oracle recommends that you disable Transparent HugePages before you start installation.
3.) Default Setting RemoveIPC=yes
Setting RemoveIPC=yes on Redhat 7.2 Crashes ASM and Database Instances as Well as Any Application That Uses a Shared Memory Segment (SHM) or Semaphores (SEM)
Recommended to follow below steps
1. Set RemoveIPC=no in /etc/systemd/logind.conf
2. Reboot the server or restart systemd-logind as follows:
# systemctl daemon-reload
# systemctl restart systemd-logind