HDTune benchmark difference between two identical 2.5 WD HDDs in good condition.

Oct 13, 2018
I have a question regarding the outcome of running HDTune benchmark on two identical 2.5 WD HDDs.

Both drives are passing S.M.A.R.T., no errors/warnings, in general they appear to be in good condition.

However, there's one interesting difference when it comes to the blue line.

Here are two screenshots of benchmark for each drive:

One hard drive seems to produce a very wavy pattern, while the other one appears to be a lot more stable in that regard.

HDTune was running from Hiren's Boot CD, so neither is a OS drive, both were low-level erased, I tried swapping them to ensure it's not caused by faulty SATA port - always the same result.

Given the fact that those are identical models, where does that difference come from?

Is this caused by one of the drives being "less ideal" when it comes to it's mechanical parts, but still within acceptable range?

Could this be an indicator that the "less stable" drive is more likely to fail in the future compared to the other drive?