I was using the ES File Explorer app, when I noticed there's many different folders with all the same content. Like, there's a "legacy" folder, a "0" folder, and an "sdcard" folder, and it all goes to the same place where my DCIM is and such. I'm wondering if whatever I have takes up three times the space, or its all shortcuts to the same place. I'm confused with all this folder nonsense.
Because of how Android has evolved over the years many newer devices have the same files mounted (usually with a bind mount) in multiple places. Others are symbolic links. It's really too bad that the file manager app isn't showing you these details :-/
Prior to ICS, Android used
/system/mnt/sdcard as the point for mount.
Some versions by manufacturers used
ICS, thereafter, changed it, but kept existing mount point for backwards compatibility with legacy apps.
/system/storage/sdcard1, particularly, JB on tablets, is used to accomodate multiple user accounts.
Crucial point is the name or alias for external storage is
sdcard for legacy reasons and will stay that way. Or in technical parlance, symbolic link in filesystem terms points to
Usually, 0 represented internal storage, 1 represented external storage.
The increased trend in dropping SDCard at expense of cheaper to manufacture rewriteable flash drives, bigger capacities, is prevalent.
I don't know about "legacy" or "0", but /sdcard is a symbolic link to the sdcard device folder.
At the terminal, run "ls -l". Add the end of some lines, you will see:
sdcard -> /mnt/sdcard etc -> /system/etc
and maybe others depending on your setup. This is standard Linux setup, and makes both places link the same place - so there is no duplication.
It is not exactly true that they go to the same place. The "0" folder as you call is is what is actually stored on the phone. So if you have your camera taking pictures and storing them on the device as opposed to the SD card, you will see those pictures (DCIM folder) under /storage/emulated/0/DCIM. Under EXTSDCard you will see things stored on your removable card.