The scope uses single shot DMA mode. A single DMA transfer is limited to 2^24 bytes due to some addressing limitation.
However the Linux driver supports continues DMA transfers using the MMAP interface.
If you use decent sample rates you can write more continues samples to a file.
An example can be found here:
https://github.com/analogdevicesinc/iio-fm-radio
Using the new libiio
http://wiki.analog.com/resources/tools-software/linux-software/libiio?s[]=iiod
With it's network back-end you can stream samples over the network and write them into a file on your x86 box. So you're not limited to the file-system size limitations and SD Card write speed.
Also we're working on a MATLAB libiio client allowing you to stream directly into MATLAB.
-Michael