Does this mean you lose all the data on your SD card? I have the same issue (my sd card is NOT set up as portable currently). I have been told my problems (my phone not accepting my SD card anymore and ejecting it after seconds) will go away if I set it up as portable instead. My problem is that I have photos on my SD card that I do not want to lose and can't currently download onto my phone (because of the issue mentioned above) and can't download onto computer as the computer won't recognize the card.
Any help will be GREATLY appreciated!!!
No, you will not lose anything... Clearing data on Media Storage and External Storage removes the databases that MTP USB Connection and other services in the phone use to keep track of the files and their location in the device, when the device is rebooted these are automatically rebuilt.
The worst thing that I have seen happen is if you have non-system sounds defined for ringtones, alarms, notifications, etc. the system temporarily loses track of them, the files are still there but the system doesn't know it, and resets the sounds to default, or sometimes to None (not cool for alarms, made me late for work one day), because they don't exist in the media database anymore. You may have to manually reassign them after the databases are rebuilt.
Remember that we do not have direct access to storage anymore, USB Mass Storage was removed from Android several versions ago, so our access is emulated through MTP or PTP, which requires database files to know what files are where. That is why clearing data on these "apps" can fix these access issues because it forces the system to rebuild those databases. This can also help other things, for example, sometimes if you add a sound to /storage/{sdcard}/Alarms and try to set, it doesn't show up in the list of available sounds, clearing data on these apps and rebooting often corrects that by rebuilding the databases properly.
To be honest though, your problem sounds bigger than just a connection issue... You may have a bad card or corrupt one. I would remove it from the device and connect it to a card reader and copy all the files off that way and reformat the card. Although with the price of micro SD cards, it might be smartest to just replace it to avoid possible data loss in the future.