AWS d3.4xlargevsAWS d3.8xlarge

d3.4xlarge pairs 16 vCPUs with 128GB of RAM at $1.9980/hr On-Demand (about $1439/mo at 24×7). d3.8xlarge pairs 32 vCPUs with 256GB at $3.9955/hr (~$2877/mo). d3.4xlarge is 100% cheaper per hour than d3.8xlarge ($1.9975/hr gap).

Because both instances are in the **d3 family**, the only thing that changes between them is sizing — same silicon, same architecture (Intel Xeon (x86_64)), same burstable/sustained behavior. The choice is purely about how much capacity you actually need: d3.4xlarge gives you 16 vCPUs and 128GB of RAM, d3.8xlarge gives you 32 vCPUs and 256GB. AWS scales pricing close to linearly within a family, so picking the right size is mostly about right-sizing your workload, not getting a better deal per vCPU.

On raw price-per-performance, the two are d3.4xlarge delivers ~106% more single-thread Sysbench score per dollar (547 vs 265 points per $1/hr). That's the cleanest signal we have for "which one runs your workload faster per dollar," but it only matters if your workload is single-thread-bound; for parallel workloads the multi-core scores (13455 vs 26155) are what to weigh. Spot pricing flips many of these comparisons — when d3.4xlarge drops to $0.7603/hr and d3.8xlarge drops to $1.1133/hr, the cheap-per-hour winner can swing meaningfully.

In practice, pick d3.4xlarge when your workload is closer to storage-optimized (HDD) (dense, sequential HDD storage — HDFS, MapReduce, log warehouses). Pick d3.8xlarge when it's closer to storage-optimized (HDD) (dense, sequential HDD storage — HDFS, MapReduce, log warehouses). When neither side is obviously right, the cheaper hourly rate usually wins for fault-tolerant batch workloads, while the higher single-core score usually wins for latency-sensitive web traffic. The regional pricing tables linked from each instance page below show where each is currently cheapest — sometimes a >20% regional gap flips the comparison entirely.