Re: Performance variation in traditional HDDs?

On 5/3/25 04:33, Nick Neumann wrote:
> Here's another CMR drive (https://pcpartpicker.com/product/6FQcCJ).
> Here, two identical drives with same model number and firmware show
> about a 10% difference in performance.
> 
> Looking at the average full drive write speed we saw the following
> results in MB/s:
> 
> Drive 1: 153.86, 153.86, 153.86
> Drive 2: 140.63, 140.64, 140.65
> 
> Again, each individual drive is incredibly consistent in its
> performance. But drive 1 is over 9% faster than drive 2. And the
> graphs of bandwidth over time for a full write are markedly different:
> 
> https://cdna.pcpartpicker.com/static/forever/images/content/684ce1fea2858681575fb7666b8b987f.png
> 
> Reporting benchmarked performance for HDDs is problematic when there
> is variation like this between two of the same drive.

I am not sure what the specsheet for this drive claims is the maximum
performance and if that checks out with your tests.

But some variation from disk to disk happens because of the variations between
heads & media that happen at manufacturing time (head SNR differences etc). How
much variation is allowed completely depends on the design manufacturing
tolerances. For enterprise class drives, this is generally tight (e.g. +- 5%),
but for consumer drives this tolerance may be relaxed, which seems to be the
case for this drive as you are seeing nearly a 10% difference.

This is a general comment. The tolerances applied completely depend on the drive
vendor and disk model. I cannot comment on a specific drive model.


-- 
Damien Le Moal
Western Digital Research