Lots of unused memory on EL6 compared to EL5

Solution 1:

These are entirely different operating systems. So behavior on one doesn't necessarily mean the other will show the same characteristics. You have to consider:

• Different kernel generations...
• Substantial changes to schedulers.
• Vastly different compiled-in defaults.
• sysctl.conf settings are different.
• Package/application config files are different...
• Different default filesystems.

The first thing to know about tuning or building an EL6 system is to take advantage of the basic system profile tuning framework. The utility for this is called tuned-adm. Red Hat's documentation is here.

The basic overview of the profiles is:

This may help you eliminate duplicate work as you modify settings. What type of application is running on this system?