Where phpstorm indexes located? And how to change location path? I have small space on internal hdd. Therefore I use external hdd.
My phpstorm projects are located there. 
If external hdd has been reconnected phpstorm project needs to be reindexed.
It takes too much time. Seems indexes are located on internal hdd.
Is it possible to store indexes on external hdd? How to set it up?

UPDATE:
here is my properties file

idea.popup.weight=heavy
idea.dynamic.classpath=false
swing.bufferPerWindow=false
CVS_PASSFILE=~/.cvspass
idea.smooth.progress=false
idea.max.intellisense.filesize=2500
apple.awt.fullscreencapturealldisplays=false
idea.cycle.buffer.size=1024
java.endorsed.dirs=
com.apple.mrj.application.live-resize=false
sun.java2d.noddraw=true
idea.jars.nocopy=true
sun.java2d.pmoffscreen=false
idea.use.default.antialiasing.in.editor=false
ide.mac.show.native.help=false
idea.no.jre.check=true
idea.fatal.error.notification=disabled
apple.awt.graphics.UseQuartz=true
idea.no.launcher=false
JVMVersion=1.6*
native.mac.file.chooser.enabled=true
sun.java2d.d3d=false
apple.laf.useScreenMenuBar=true
Adjust the settings in this file: 

IDE_HOME\bin\idea.properties


Change these options: 


idea.config.path 
idea.system.path 
idea.plugins.path 
idea.log.path


My Source:
https://intellij-support.jetbrains.com/hc/en-us/articles/206827407-Changing-IDE-
default-directories-used-for-config-plugins-and-caches-storage

Here is some additional information:
https://intellij-support.jetbrains.com/hc/en-us/articles/206827437-Directories-used-by-the-IDE-to-store-settings-caches-plugins-and-logs