Cassandra uses immutable SSTables. When data is updated or deleted, the old version remains on disk alongside a new version. What are the primary performance impacts during 'Compaction'?

1. A Compaction is purely a memory-cpu task and has zero impact on Disk I/O or storage space.
2. B Write Amplification and I/O Contention: Merging multiple SSTables into a single new file consumes significant Disk I/O and temporarily requires enough free space to hold two copies of the data.
3. C Compaction speeds up writes by clearing the Memtable every 10 seconds.
4. D It is only required when the database is using a relational storage engine behind the scenes.