External SD write protection

Starting with Android 4.2/4.3, apps granted READ/WRITE permission to device's storage do not actually get those permissions on any external storage, be it an SD card or an USB OTG ! Those permissions only apply to internal storage.

Starting with Android 5.1, apps can acquire write permission through SAF (Simple Android Filesystem), which requires user to manually grant access from a specific folder (or root) of each external storage.

More information can be found here:

• Fixing external SD card write issue on Android 4.4 KitKat
• [Fix][N9005][ExtSdCard Write Issue][Kitkat 4.4.2][NA6] - Rooted
• Is Google blocking Android apps from writing to SD cards?
• How to Bypass Android 4.4 (KitKat) External SD Write Restrictions Without Root