Hey, explain me this. If i use shadownand, i will need SD card just to to install cias (it implies boot without SD) ? My saves and games will really be stored on internal memory? I'm having some SD problems here, and need to lower the SD constant reading and need...
No.
Most savegames would be stored on the game's cartridge. (Some games store it on the SD even with a cartridge)
However if you installed the game as a CIA (or loaded it from the eshop) you obviously dont have a cartridge. In that case it will be stored on the SD Card.
Gamed downlosded from the eshop or indtalled as CIA are saved on the SD Card as well (unique encrypted).
If you remove the SD Card you'll not have access to these. (Or themedata or any extdata).
They can't be stored on the NAND because the NAND would not have enough size to store it.
There are different NAND chips used with different sizes for 3DS systems.
The biggest NAND chip is 1888MB.
In case of a 2DS the actual NAND partition etc requires 942MB (N3DS requires 1238MB - and O3DS only has NAND chips below 1000MB).
This would give you about 900MB space with for a 2DS with the biggest NAND chip (let's call this "best case szenario).
And this would barely be able to hold 1 Game in this "best case szenario".
For comparison a Monster Hunter Game requires 1.5GB.
Not even talking about the accessability changes required to make it work.
This simply installs a small CFW setup onto the NAND so you have the most basic patches.
If you are a pirate this is not useful for you.
It's just nice to have if you forget your SD Card and have game cartridges. Then you can stil play.
Or in the case of the 3DS' SD Card reader breaking or something like that.
TL;DR: Savegames and Games are not stored on your NAND Chip. You still require a SD Card. But you are able to boot without an SD Card and play Cartridge Games.