Yes, it seems like Cassandra is suffering from compacting too, although maybe not so ugly as LevelDB.
The only solution I've found is Castle backend from Acunu [1], but there were no updates from 2011 [2] and it looks really heavy (with kernel module and all that)
Isn't that a problem common to all SSTable-based databases?
Is LevelDB any worse than HBase or Cassandra in this area?