Something is secretly eating up my Acer Iconia A500 internal memory and I need help finding it

I've been a happy owner of an Acer Iconia A500 for a bit over a year now but a couple of weeks ago it started to complain about its internal memory being full. I was a bit surprised as I keep movies, and such on the external SD card but I assumed is was some browser cache, Maps or so which had eaten up a fair chunk of the 32G memory it has internally.

However, that doesn't seem to be the case. I have cleared the data of almost every single App I have installed but still if I look at the Storage tab of the settings I see the following (a couple of hours ago):

I get the feeling that the rightmost grey part of the bar should be a bit more than 379MB(the Available part)... (SD Card at the bottom of the picture is the external one, never mind that one).

I've tried almost every disk usage app available out there and they all show similar results, the following is DiskView (picture taken after I removed a few apps):

(in this picture "SD Card" is the internal one...)

One thing all the disk usage apps seems to have in common is that unless the device is rooted, they cannot see what is in some directories (like /data) which makes me think it is either Android itself (4.0.3 on this device) which has some kind of cache which is misbehaving or that some process is producing extreme amounts of logs somewhere.

Sorry for this long intro, but the basic question is: How do I proceed?

I guess one alternative is to find what is worth backing up and do a factory reset or something but I wold really like to find out what happened first.

Rooting it is an alternative which would probably help me find out more but I sort of like it as it is (except for this issue). If it is needed to resolve it I could of course do it but it feels like you shouldn't have to with an appliance like this.

Is there another way forward? I have this naive hope that there is a button somewhere I haven't seen that clears all logs or reduce the log level from debug to info.

Edit: One thing I've been considering but cannot investigate is if it could be cores. I've had a lot of crashes lately (presumably because it has been running low on disk).
In response to Izzy's comment below. Apps adds up to more or less exactly the 700MB listed as "Apps" (seems to be the total of data and the apps themselves).

Answer

This looks like the Acer GPS-log leak we had on an Acer Iconia A200:

The bottom line is that when the GPS is used, the GPS driver for ICS 4.0.3 on the Acer A-series tablets apparently writes numerous gl-YYYY-MM-DD-HHMMSS.txt files into the /data/gps directory. The files are apparently not automatically deleted, and so over time will consume most of the internal storage space.

Users can not delete these files without root access. However, there is a patch to clear the GPS log data (no root access needed, so no warranty voided).

• download the patch from the Acer drivers site (to your desktop)


• unzip and copy the contained Update.zip from it to an empty, FAT32 formatted microSD card. (We uploaded it to an already present card in the connected tablet, which wasn't empty, but it still worked.)


• (Re)start the tablet with the microSD card in it, while holding the “Volume Down” key until a message appears in the upper left corner of the screen.
  (Something like Erasing cache before SD update...; I interpret this message as: "erase and update", so it should cure the symptom and the cause.)
  The tablet will continue to start up afterwards (less than a minute), and you will be good to go.

There is a nice .pdf in the download, describing the above steps in detail with (screen)shots. (It also talks about an accompanying user_cleanGPSlog text file, but we didn't have it and did not seem to need it.)