Q:

Why is my index directory so small when fields are compressed?

The answer probably lies in the question, but I would like to make it sure anyway :-)
I indexed 10000 documents. Each has a field which stores a text which is exactly 100KB big (it comes from a text file which uses UTF-8). When this field is uncompressed then the index directory is 436MB big, but when the field gets compressed then it's only 11,4MB. That would be a compression ratio of 37,5 - that's too good to be true or is it not? Or is it possible that the data gets stored somewhere else on my computer aside from the index directory? 
When I retrieve the field then there are no errors. Everything is fine, but I surely know from life that if something is too good to be true, then there is definitely something wrong :D
Here's the code:
// RAW, NOT SEARCHABLE
FieldType fieldType2 = new FieldType();
fieldType2.setIndexed(false);
fieldType2.setTokenized(false);
fieldType2.setStored(true);
fieldType2.setOmitNorms(true);
fieldType2.setIndexOptions(FieldInfo.IndexOptions.DOCS_ONLY);
fieldType2.freeze();
Field raw = new Field("Raw", CompressionTools.compressString(text), fieldType2);
doc.add(raw);

A:

The author of compression feature suggests he got even bigger improvement: 76M -> 1.7M so your results are comparable.
And yes, Lucene does not write files outside configured directory, that would be a major bug.

