CrystalDiskMark is a small HDD benchmark utility for your hard drive that enables you to rapidly measure sequential and random read/write speeds.
WD Black WD4001FAEX 4TB:
Seagate ST4000DM000 4TB:
Benchmark Results: With Crystal Mark v3.0.2f run with a file size of 1000MB the WD Black 4TB hard drive has impressive sequential read and write speeds of just over 150MB/s. Not to be outdone the Seagate 4TB desktop hard drive also ran at speeds just over 150MB/s on the sequential read and write benchmarks. The two 4TB drives also have similar performance at both 512K and 4K file sizes.