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Comment by daymanstep | Hacker News Reader

HDDs also lose magnetic charge over time, about 1% per year. So you need to periodically spin up and rewrite the data every few years.

CD drives however, can store data indefinitely without needing refreshing.

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But the materials on the CD eventually break down, sometimes as soon as within 5 years. So you can look into MDisc, which purports 100 years…but only in theory since the tests are just approximations of what would actually happen.

Totally could be a defect in the lamination we don’t find out for years yet

The important distinction here is that CD-ROMs can store data indefinitely, but CD-Rs and CD-RWs can not.

BD-R and M-Disc CD and DVDs have archival storage life.

CD-R media is of limited shelf life as well though

As an industry insider, I have never heard the one percent. I'm not saying that it's not possible, but I don't recall ever hearing of us testing for it. So what is the source of the 1%?

Having had drives which sat for many years and spun right back up without corruption makes me think 1% is too generous maybe 0.05% per year at most

The claim you're responding to is that hard drives lose "magnetic charge" at a rate of 1% per year, not that bits get corrupted at a rate of 1% per year. The error correction in hard drives is far simpler and weaker than what's used in SSDs, but it does exist. So we should expect that there's a significant margin for data degradation before any observable data corruption begins. (This is true for SSDs, too; the first symptom of data degradation is reduced read performance as slower, more complex error correction methods kick in, then much later the host starts to actually get read errors or bad data.)

The magnetic strength of particles on the disk can decay at 1% per year, but the drive won't have issues reading them until they fall below a threshold where they can no longer be read. It could take decades.

Magnetic HDDs also tend to have inbuilt SMART features to monitor disk performance and health, so they can inform when they are beginning to give problems. So the advanced user can recover the data before the HDD fully fails.

In my experience, flash drives tend to get problems suddenly leading to data corruption, and it may not be immediately apparent to the user till it is too late. I haven't such problems in recent years though, so maybe flash drives have become smarter too.

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