Understanding Storage Distinctions Accessible from Application.persistentDataPath in Unity

The path you can get from Application.persistentDataPath should be /data/com.xxx.xxx/files, but AndroidManifest.xml has

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

As it says, the terminal writes data to the main body and writes it to SD CARD.

Does anyone know how to tell if Unity is currently writing data or SD CARD?(The reason I want to know is that when I download the file, I check the error that there is no space, but I want to check it before downloading it and let the user know.)

I can get the empty space of the unit and if I have SD CARD, but I don't know where Unity is writing, so I don't know where to look when I check the capacity.