Write-optimized databases and flash storage have arrived. Moving from disk to flash is usually easy. Changing a database implementation has much more uncertainty when that includes moving from the well-understood B+ Tree algorithm as implemented by InnoDB to a write-optimized algorithm like a Log Structured Merge tree as implemented by WiredTiger, LevelDB and HBase. I did such comparisons on paper and using real implementations. I will describe what I learned and the framework I developed to describe and compare the alternatives. My focus is on storage efficiency.