Throughput Optimized HDD (st1) is the correct and most cost-effective EBS choice because the workload reads and processes large log files sequentially. AWS defines st1 volumes as low-cost magnetic storage designed for frequently accessed, throughput-intensive workloads, including log processing. This workload does not require high random IOPS or ultra-low latency, so gp3 and io1 would be more expensive than necessary. Cold HDD (sc1) is cheaper but intended for less frequently accessed data, so it is not appropriate for an active log-processing application. Because the company wants minimal architectural change from SAN-based block storage, an EBS volume preserves the block-storage model while meeting the sequential throughput requirement.