Factory reset on merged storage - Shall I lose my data
According to the article  Reset your Nexus device to factory settings (Nexus 5 and Nexus 9 listed too) by Google,


  By performing a factory data reset, all data will be erased from the device. While any data stored in your Google Account will be restored, all apps and their associated data will be uninstalled. Make sure you back up your data before you do a factory data reset.


The testimony of a Nexus 4 owner, coupled with supporting arguments from other Reddit users confirms that factory data reset will nuke everything. 

As per AndroidPIT on How to factory reset the Nexus 5 for better performance


  Since the release of Android 4.4, the ‘factory data reset’ option (accessible in the settings menu) performs the same job as a ‘hard’ reset. All of your user files, apps, etc will be deleted and your device will revert to a factory fresh state.


Their hard reset is not our hard-reset but our factory-reset using recovery mode.

Guide To Perform Hard Reset Android HTC Nexus 9 on guidebelajar blog (has useful screenshots) confirms that factory data reset for Nexus 9 would also remove every user file created or moved into the device.



As per the article How do I reset my phone? by Motorola


if you decide to factory data reset using Settings app, you would be given a choice to erase media (files under /data/media/ such as music, videos, pictures),
should you decide to boot into recovery mode, everything would be deleted


The information is also valid for Moto G (1st Gen, 2nd Gen, 3rd Gen) family of devices.

(That's all for now)