Full seek on a modern drive is a lot closer to 25ms than 8ms. It's pretty easy to test yourself if you have a hard drive in your machine and root access - fire up fio with --readonly and feed it a handmade trace that alternates reading blocks at the beginning and end of disk. (--readonly does a hard disable of any code that could write to the drive)
When I was reviewing it for publication I ran a couple of tests and found more like 18 on the devices I tested, but I’m sure there are some that do 15. 25 is probably on the slow end. (although I’ve never tested a HAMR drive - their head assemblies are probably heavier and more delicate)
Old SCSI 10K drives could hand a huge queue and reach 500 random read IOPS, sounding like a buzzsaw while they did it. Modern capacity drives treat their internals much more gently, and don’t get as much queuing gain. Note also that for larger objects the chunk size is probably 1+ rotations to amortize the seek overhead.
Oh, and by “full seek” I mean the time it takes to read the max block number (inner diameter) right after reading the min block number (OD) subtracting rotational delay.
You can do this test yourself with fio —readonly and root access to a hard drive block device, even if it’s mounted. (good luck reading any files while the test is running, but no damage done) Pick a variety of very high and low blocks, and the min delay will be when rotational delay is close to zero.
Here's a good paper that explains why the 1/3 number isn't quite right on any drives manufactured in the last quarter century or so - https://www.msstconference.org/MSST-history/2024/Papers/msst...
I'd be happy to answer any other questions about disk drive mechanics and performance.