arcgis 10.3 - Fast way to merge 8000 raster?

I have to merge almost 8000 rasters (TIF).

I tried using Mosaic To New Raster in ArcGIS 10.3, but it's processing really slowly and crashes quite often.

Is there a faster (or more stable) way to merge 8000 rasters?

I also have access to QGIS 2.10.1, but I'm willing to try any free software.

Answer

The two easiest paths are:

1. 
   

   ArcGIS - mosaic dataset. You can read a lot about it at http://help.arcgis.com/EN/arcgisdesktop/10.0/help/index.html#//009t00000037000000
   A mosaic dataset is a very flexible approach, that may have too many options for your needs. However, it is quite good at combining imagery from many different sources and acquisition times.

   
   


2. 
   

   GDAL - gdalbuildvrt. See http://www.gdal.org/gdalbuildvrt.html for the man-page. This tool requires you to use the commandline / DOS for interfacing properly, but it will quickly make a "virtual raster" which functions as a regular raster, but doesn't take up the same amount of space etc., by simply pointing at your many rasters, instead of creating a new copy.

   
   

Both of the approaches delineated above can be exported into a big raster, once they have been applied.

PS. it may be possible to interact with gdalbuildvrt through QGIS, but I am not certain that it is possible to do it in an efficient way, when dealing with 8000 rasters.