Re: Performance variation in traditional HDDs?

Just a quick update on initial test results. We started with the two
"identical" drives (https://pcpartpicker.com/product/BcQG3C) that
showed the largest difference. Note these are SMR drives so we are
careful to do an "ATA SECURITY ERASE" before running our benchmark.

Previously we had these drives sitting vertically in 3d-printed trays
during our benchmarking. We moved to benchmarking them mounted
horizontally with screws and vibration dampening pads. They were
mounted to a heavy metal "open air" style case. Drive 1 was
benchmarked, then Drive 1 was removed and Drive 2 installed in the
exact same location as Drive 1, and then Drive 2 was benchmarked.

We didn't see any real difference in results when changing to this
traditional mounting. Drive 1 went from an average full-write
throughput of 174.06MB/s to 174.08MB/s. Drive 2's average full write
throughput stayed at exactly 157.88MB/s.

Looking at a graph of throughput over time for the
differently-behaving but identical drives is really interesting:
https://cdna.pcpartpicker.com/static/forever/images/content/13b2fa7e147ddd5359f5638b4efde7af.png

We're working on making sure our HDD mounting is adequate. Do you have
any specific guidance/tips on what should be done? Is the goal of the
mounting to prevent outside vibrations from affecting the drive,
dissipating internal vibrations, or both? We use a number of identical
3U rackmount machines for our SSD benchmarking and would also like to
leverage them for diving into this HDD issue in more depth, but they
do not have traditional HDD mounting locations. So for now we are more
slowly conducting experiments on one of our open-air dev benchmark
machines, which has proper mounting locations.