Final answer:
SSD (Solid State Drive) is the recommended hardware feature for cost efficient performance on an Hadoop datanode.
Step-by-step explanation:
The hardware feature on an Hadoop datanode that is recommended for cost efficient performance is SSD (Solid State Drive).
SSDs offer faster read and write speeds compared to traditional hard disk drives (HDDs). This allows for quicker data access and processing, which can improve performance and efficiency in a Hadoop environment.
Additionally, SSDs consume less power and generate less heat, leading to lower energy costs and better cooling efficiency.