Hi Jonathan,
 
May take a look at the function "clusterR" from the raster package, this function does the mosaicing you are writing. And for what I know this doesn't imply that data is written trice because the single tiles remain in memory.
We put much efforts to reduce the traffic of data in the parallel enabled raster function.
 
I hope this helps, Matteo 
  

>>> Jonathan Greenberg <jgrn@illinois.edu> 2/17/2012 4:20 pm >>>
R-sig-hpc'ers:

I've started running R on a large cluster at my university, which uses the
IBM GPFS parallel file system.  I'm wondering if there is any support
within R for parallel writes to a single file or if there are any
suggestions on to the implement, say, writing to a large binary file
representing an image.  The parallelization I'm thinking of is:

given an image of x by y columns and rows represented by a flat binary
file, process chunks of this image on different cpus/nodes, then write the
results to a single file.  The alternative is to write each chunk out
separately then "mosaic" them back together, but this would involve
reading/writing the data twice, and this process is going to be an I/O
intensive one.  Thoughts?

--j

-- 
Jonathan A. Greenberg, PhD
Assistant Professor
Department of Geography
University of Illinois at Urbana-Champaign
607 South Mathews Avenue, MC 150
Urbana, IL 61801
Phone: 415-763-5476
AIM: jgrn307, MSN: jgrn307@hotmail.com, Gchat: jgrn307, Skype: jgrn3007
http://www.geog.illinois.edu/people/JonathanGreenberg.html

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