So I've been researching this issue for a long long time and have tried so many different approaches. I've finally found one that works! You can now save your google play music to your external sd instead of the internal sdcard.
This is based on the post found here. Please go and thank the original author. This will probably work on any phone.
So what this basically does is mount the google play music cache to a directory on your external SD on boot.
2. external SD(obviously)
- Using whatever task manager you have or just go into settings->apps->running, close google play music.
- Open your file manager and browse to /sdcard/Android/data/com.google.android.music/cache and delete all of the files found in music dir and artwork dir in this directory. This is very important step. If you do not delete your cache then your files will take up space but will no longer be available after this process.
- Browse to the root diretory of your external sdcard and create a directory called "MusicCache".
- Browse to the root of your internal sdcard and create a text file called "MusicScript.txt".
- Using your favourite text editor open the the file and past the following: "mount -o bind /emmc/MusicCache/ /sdcard/Android/data/com.google.Android.music/" and the save the file. Please note that if your using stock room, then /emmc/ might be /external-sd/. Please make sure to check the directory name for your external sd and replace /emmc/ with whatever your external sd directory is named.
- Go to the google play store and install script manager - Smanager. Open smanager, and on first open you should see an option to select root, check that option and click ok and make sure to grant root to the app when the su dialog appears.
- In Smanager browse to the root of your sdcard and click on and hold the "MusicScript.txt" to open a options dialog. Select "open as" and then select "Script/Executable".
- Then Select "Su" and "Boot" and hit save.
- You might not need this stop but it might solve some issues. Go to settings app->apps->google play music-> and hit clear data.
- Reboot your phone.
- Open up google play music and click on Choose on device music, and you should see the total space available equal to what is available on your external SD Card
- (Optional) Hamster dance.
Note: While downloading all of your music offline you may want to go to the settings app->developer options->check Keep Awake to keep the phone awake while charging so that the phone won't go to sleep. I did this so that I could finish up the download while keeping my phone charger connected. You should definitely turn this option off after your done.
**I assume no responsibility if this damages your device in any way**