Mastodawn

Dave Anderson Aug 12, 2025

Digging into the drive in my NAS that faulted, I'm reminded that magnetic hard drives are preposterously magical technology.

Case in point, using Seagate's tools I can get the drive to tell me how much it's adjusted the fly height of each of its 18 heads over the drive's lifetime, to compensate for wear and stuff. The drive provides these numbers in _thousandths of an angstrom_, or 0.1 _picometers_.

For reference, one helium atom is about 49 picometers in diameter. The drive is adjusting each head individually, in increments of a fraction of a helium atom, to keep them at the right height. I can't find numbers of modern drives, but what I can find for circa ten years ago is that the overall fly height had been reduced to under a nanometer, so the drive head is hovering on a gas bearing that's maybe 10-20 helium atoms thick, and adjusting its position even more minutely than that

This is _extremely_ silly. You can buy a box that contains not just one, but several copies of a mechanism capable of sub-picometer altitude control, and store shitposts on it! That's wild.

Anyway my sad drive apparently looks like it had a head impact, not a full crash but I guess clipped a tiny peak on the platter and splattered a couple thousand sectors. Yow. But I'm told this isn't too uncommon, and isn't the end of the world? Which is, again, just ludicrous to think of. The drive head that appears to have bonked something has adjusted its altitude by almost 0.5 picometers in its 2.5 years in service. Is that a lot? I have no idea!

Aside from having to resilver the array and the reallocated sector count taking a big spike, the drive is now fine and both SMART and vendor data say it could eat this many sectors again 8-9 times before hitting the warranty RMA threshold. Which is very silly. But I guess I should keep an eye on it.

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Keith Judge Aug 12, 2025

@danderson Another astonishing thing about HDDs is that in the early 2000s, when most HDDs were 3.5" or 2.5" desktop or laptop things, someone was able to figure out how to mass produce HDDs small AND robust enough for the iPod and similar devices.

At least until flash memory became affordable enough to overtake these micro HDDs.

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Inga stands with 🇺🇦 🇵🇸

@KeefJudge @danderson ipods and similar devices don't have a very high needs for robustness. At typical HDD data transfer speed, and at typical compressed audio bitrate, you only need HDD running for like a handful of seconds per hour (running HDDs constantly would destroy these devices' batteries).
And with all kinds of gravity sensors, the players only need to find a small moment of calm to spin up the HDD and to read one buffer worth of compressed file data from it.

Just like, before HDD players, it was the same with audio CDs (although their buffers were usually limited to something around a minute, and CD reading speeds were at most 10x the audio stream bitrate). When subjected to constant shaking they couldn't work, but in real life conditions their sensors usually could find enough calm time to spin up the CD and read data off it (even when players without anti-shock feature struggled to work). Although of course players with larger anti shock buffers, or MP3-CD players, worked better.