Android 6.0, backing up SD card before reformatting I use Vodafone Tab Prime 7 (Android 6.0.1; hardware remotely based on Alcatel One Touch) with 32GB Samsung SD card (almost 30 gb full). I was using in for a few months but now with all my apps installed (many of them moved to SD card), my android started to be rather slow and it often happens that it restarts on its own or gets stuck with apps that are on the SD card. I want to reformat my SD card (and in the same time clear some garbage) but I do not want to lose my apps (nor I do want to install them all over again, there is many of them). My plan is to move all the files on the SD to a computer, but because the SD card is formatted as an internal partition I am not able to do that. 

What is the best way to back up all my data on SD card, and put them safely back after I reformat the SD card (which I suppose will fix half my problems, correct memory errors atp.)? 

Can I simply copy them via Android-PC usb connection? (I am not sure if it will copy all the necessary data). And if I would somehow set the sd card as external, copy all the data to PC, would there be a way how I could put all those data back after reformatting the card? 

I will probably figure it out somehow, but I would like to know more secure ways of doing it.
As you state that 


  some content is visible, but I doubt that its all


I assume that by the means of tablet your card is visible and accessible. You doubts about incompleteness of displayed files are groundless, because usually most of the app data is hidden, that's why you don't see it.

I see two solutions here:


Install TWRP or any other custom recovery which allows doing full NanDroid backup.
Steps for making backup in TWRP are quite simple and described in many tutorials, e.g. this.
Gain root on the tablet (if not having already) and make manual partition backup via ADB.


After you set up ADB and gain root access, you can make backup with:

adb pull /dev/block/mmcblk0


and restore it with

pv mmcblk0 | adb shell dd of=/dev/block/mmcblk0


where mmcblk0 is the name of your card, which can be taken from the DiskInfo, for example.

You should decide which approach is simpler for you.

P.S. I highly doubt that reformatting card will fix your errors and memory issues. Their cause seems to be in installed apps, not in filesystem.