Normally, reading and writing to multiple SATA drives at the same time isn't an issue. Each drive has their own SATA connection so the activity of one has little, if any, effect on the performance of another. That isn't the case with the Black² though. With the SSD and HDD portions of the drive sharing the same SATA interface, the performance of one is impacted directly by the other.
The benchmarks below show the the performance of the SSD and HDD portions of the Black² under a normal and heavy load. The load was generated by running Iometer in the background. To simulate a normal load, we ran a test with a mix of sequential and random reads and writes. We then simulated a heavy load by running a sequential read test that maxed out the performance of the drive.
 WD Black² SSD - Normal Load |
 WD Black² HDD - Normal Load |
Running a normal load on the SSD portion had very little, if any, impact on the performance of the HDD half of the Black². Unfortunately, the same can't be said for the SSD portion of the drive. With a normal load running on the HDD, the read and write speeds of the SSD portion dropped by as much as 89 MB/s.
 WD Black² SSD - High Load |
 WD Black² HDD - High Load |
Under high loads, the performance of both the SSD and HDD portions of the Black² dropped considerably. Surprisingly enough, the HDD portion ended up being the faster of the two.
