Does cassandra distributes keys evenly among DataFileDirectories?
If one have multiple hard-drives on a single host it makes sense to list them all there.

I tried with two DataFileDirectories

and it ended up with all the data in the first.

Cassandra does write to both of them, but
1. Writes are not evenly distributed, at one moment there are 15Gb in the first and 3Gb in the second
2. It continuously migrates data from the second to the first. So once active writing stops and server is idle, the second DataFileDirectory becomes empty

I suppose this is an effect from compacting process

1. Is it by design?
2. Is there a way to control key distribution, for the cases when hard-drives are of different capacity?