This tutorial assumes that you have read installing steam arma 3 tools page and the tools are installed. You could setup P: drive or workspace as bis calls it, without the tools put there is not much point doing that.
Setup P: Drive
Download ALL the Latest Versions of the required Mikero tools. You should install them all, but you must install these bare essentials:
Next you need to replace the mapdisk.bat file which can be found on the root directory of the ArmA 3 tools, with your own. This is because the original mapdisk.bat supplied by the tools is not working properly.
Use this for “mapdisk.bat” replacement:
subst p: /d subst p: "c:\arma3work"
Replace “c:\arma3work” directory to where you want to keep your work drive. Do not use ArmA 3 Tools directory. You obviously have to create this directory. Next just double click mapdisk.bat to activate the new P: drive.
You might have to setup mapdisk.bat into your windows startup programs so you don't have to click it every time you restart your computer and want to edit ArmA 3.
After you see the new P: drive appear in windows explorer etc, run ArmA3P.cmd and wait… ArmA3P should run all the way - with no errors, and report success. This will take really long time, be patient and wait.
When this is done, your brand new P: drive is ready for some ArmA 3 Editing