I found your solution and it is exactly what I need! Only the index is a big problem - my key's are always 32 chars long (MD5 Hash) and caused by this the index is > 250MB for just 8000 entries. But I need millions of them.
I did a test with a hashtable and i found that using a hashtable with objects only needs 4,2MB and less than 1 second for 100.000 entries incl. writing to disk. The value for this test is same like the key and is included in the 4,2MB.
Is it possible to use the hashtable in the next version?! This will speed up everything!
If you need help - just let me know!