MainStage 3.5 and newer added a new Preferences tab titled "Sampler" that includes important settings for live performance when sample-based instruments will be used.
To access MainStage Preferences, in the Menu bar choose MainStage then "Preferences"and navigate to the "Sampler" tab in the window that opens.
We recommend that you not make any changes to settings in the "Misc" tab.
We then recommend that you click the "Virtual Memory" tab and ensure the following settings are in place (also visible in the screenshot below):
"Active" selected.
"Buffer Range" set to "Small".
"Host Disk Activity" set to "Less".
For the vast majority of users the above settings will minimize MainStage's demand on your computer's RAM while also ensuring that all needed samples will be streamed from your hard drive when needed.
If your hard drive is an older, spinning hard drive, not a solid state drive, then we recommend making the following changes:
"Buffer Range" set to "Medium".
"Host Disk Activity" set to "Average".
For additional help, check out these articles:
Working Around MainStage 3.5 Bugs/Issues