Comment Writeback was the killer feature (Score 1) 94
But on Linux? The software RAID controller was faster. The job is I/O bound, not CPU bound.
The good RAID controllers had a battery-backed writeback cache, which would make transactional workloads (lots of fsync) much faster by reordering across write barriers. It's an order of magnitude faster in many cases.
You can't do that without battery-backed memory to replay the transactions after a power loss. Memory-only cards did exist, but they were rare and proprietary. In practice 99% of people who needed this just used a hardware RAID card.