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Build a 100.000.000 by 10 element SparseArray.
Fill position 1/1 and 100.000.000/10 with a value 999.999.999.999.999. 

num = 999999999999999;  
idSparse = SparseArray[{{1, 1} -> num, {100000000, 10} -> num}];

Look for RAM usage. 

ByteCount[idSparse] 
976

Export it to a file 

Export["idSparse.rsa", idSparse];

See the disk usage. 

FileByteCount["idSparse.rsa"]  
205000360

Is it OK like that?
Two elements only occupied. For file usage is very high compared with RAM usage.

corey979
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Hp Radojewski Schäfer Von
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  • I can't reproduce your observations: as one would wish and expect, the file seems to be the same (small) size no matter how large the array nominally is. I tried in version 9.0.1. Which version are you using? – Oleksandr R. May 19 '13 at 01:42
  • The two numbers 976 and 205000360 are mixed up. . .Sorry. . .So file size is small and RAM usage is large. – Hp Radojewski Schäfer Von May 20 '13 at 12:06
  • There is definitely something strange here, and the memory usage is much higher in version 9 than in previous versions. This would be a good question if you would edit it to focus on the memory usage rather than the file size. When you do so, you'll have my upvote. – Oleksandr R. May 21 '13 at 01:49

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