Last month i have big problems with .thumbdata-6549877559 files which is automatically created in dcim/.thumbnails folder, after factory reset.Often this files eat whole free spce in internal memory, and then strat corruption of files, slowdowns etc. I tried many solutions online, and finally found 
. BTW my .thumbdata are using over 2gb internal memory because i have lot of pictures on external sd. Not any more 
Simple solution is to delete .thumbnails folder, and create .thumbnails file with filemanager, or any other file explorer. Remember, u must do it on phone, on PC u cant create file that begin with "."\
After that Android cant create folder with same name like file in same folder, and your DCIM folder remains perfectly clean.
Over a month of usage, i dont have any problem with this solution, everything work normally.
share this to those who worries on this...
. BTW my .thumbdata are using over 2gb internal memory because i have lot of pictures on external sd. Not any more Simple solution is to delete .thumbnails folder, and create .thumbnails file with filemanager, or any other file explorer. Remember, u must do it on phone, on PC u cant create file that begin with "."\
After that Android cant create folder with same name like file in same folder, and your DCIM folder remains perfectly clean.
Over a month of usage, i dont have any problem with this solution, everything work normally.
share this to those who worries on this...
