Sooner or later most Android smartphones users notice, that their storage is slowly eaten up by "something". Closer inspection will reveal that in the DCIM/.thumbnails folder one or more, .thumbdata files are stored. They can have size from few MBs to several GBs, which for users with limited storage can be pretty devastating.
The most common example of these files is .thumbdata3--1763508120, or .thumbdata3--1967290299 but there is probably hundreds, if not thousands variations of this file type, probably based on the type of device, versions of Android, etc. But the file names do not appear to be unique for each user.
These .thumbdata files can take up a considerable amount of space, and that is the usual reason why users notice them - because they lack space on their SD cards and they don't know what is eating it up.
So the question is, what are .thumbdata files and what is their purpose? And the following question usually is, how to get rid of these files?
This article contains information about and possible solution for .thumbdata files, gathered from various public Android tech sites and forums as well as from personal experience as Android users.
Android THUMBDATA related information
What exactly are .thumbdata files and what is their purpose?
Actually, nobody knows exactly, well except for the devs, but they didn't share their info. There are just hints and deductions, but there are no exact specifications for the THUMBDATA format atm.
As was said before, *.thumbdata files are hidden by default, so unless you have the option for showing hidden files enabled, (Menu ► Settings ► Show Hidden Files) you might not even be aware of them and that they are eating up your free space. You can find them in /DCIM/.thumbnails folder on your SD card or internal storage, depending on where your images are saved by default.
Considering *.thumbdata files are generated in the DCIM folder where the digital camera saves photos, it is likely that the *.thumbdata files are generated by apps related to the digital camera, image preview or editing. From what we could gather, the general consensus is that these files are created by any of the media gallery apps.
THUMBDATA format is used for indexing and caching purpose and probably also contains thumbnails of processed images as well. They are generated so image previews (thumbnails) are quickly loaded on the display and users do not experience any sluggish behavior when they browse through their images, especially if they have a huge library.
The problem with these .thumbdata files is that they grow with each image the gallery/camera app encounters, and thus THUMBDATA indexes can even potentially store data about images that were deleted from the device. So a situation may happen, that even if you would delete all images from your storage, one or more .thumbdata files would still take up space.
How to get rid of these .thumbdata files from the smartphone?
The very first thing most users try, is to simply delete the *.thumbdata files. This "works", but the files will be recreated rather sooner than later. They may not take as much space as before, but eventually, they will grow again to be bigger and bigger.
Some handy file manager app may be very helpful in this and you can find plenty of them in the Google Play store. This solution works, but can be rather tedious to repeat every time you need space again.
How to prevent .thumbdata files to grow big in size?
There is one, pretty reliable solution to solve the "thumbdata problem". Check out the exact file name of your .thumbdata file and write it down, let's say .thumbdata3--1763508120.
Now, delete it and create a new folder with the Root Browser app (check Google Play store) in the DCIM folder where the .thumbdata file was previously located and rename the newly created folder to the name of the original .thumbdata file, in our case the folder name would be .thumbdata3--1763508120.
And that's it. The system will be fooled, and no more .thumbdata files will be generated and eating up your free space.
Some users also tried to create an empty file with the same file name and restrict it for reading, but it apparently does not always work and some apps that synchronize images will remove the "read only" attribute. That means the "folder way" is probably the only choice at the moment how to reliably disable .thumbdata file growth.
Can images be recovered from .thumbdata files?
The short answer is no. The long answer would be, no - because there are no actual images in the .thumbdata files, so there is nothing to be recovered.