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Comment by teddyh | Hacker News Reader

> SSDs have predictable durability?

If it is not plugged in, i.e. unpowered, don’t count on anything more than three months. Thread with sources: <https://news.ycombinator.com/item?id=27573332>

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I don't understand. The only source I find in what you link is an AnandTech article which literally contains this:

"Remember that the figures presented here are for a drive that has already passed its endurance rating, so for new drives the data retention is considerably higher, typically over ten years for MLC NAND based SSDs."

It is kinda obvious that if you pass the numbers considered safe then bad things shall happen.

But a SSD sitting on a shelf starting to lose bits after three months seems incredibly low.

People don't know about that and they'd be screaming by now.

I don't think it's that bad.

> The only source I find in what you link is an AnandTech article

In that thread is also this post:

<https://news.ycombinator.com/item?id=27573332#27573720>

Which contains this link:

<https://web.archive.org/web/20210502042514/http://www.dell.c...>

Which in turn contains this text and table:

I have unplugged my SSD drive and put it into storage. How long can I expect the drive to retain my data without needing to plug the drive back in?

It depends on the how much the flash has been used (P/E cycle used), type of flash, and storage temperature. In MLC and SLC, this can be as low as 3 months and best case can be more than 10 years. The retention is highly dependent on temperature and workload.

  ┌────────────────┬─────────────────────────────────┐
  │NAND Technology │ Data Retention @ rated P/E cycle│
  ├────────────────┼─────────────────────────────────┤
  │SLC             │ 6 Months                        │
  ├────────────────┼─────────────────────────────────┤
  │eMLC            │ 3 months                        │
  ├────────────────┼─────────────────────────────────┤
  │MLC             │ 3 Months                        │
  └────────────────┴─────────────────────────────────┘

If it's eMLC, kept at elevated temperature (40C), and unpowered. Consumer drives use higher floating gate voltages so they'll keep data for a year while unplugged.

A year is still much shorter than most people assume. In my experience, most people think they can buy SSDs, put data on them and then shelve them for 20 years without issue.

I recently recovered data from a 2012 Macbook Air SSD that was powered off for 7 years with no data loss.

The source does say “best case can be more than 10 years.”. I would still not use off-line SSDs as long-term archives.

One year is the worst case scenario. Drive with used up total bytes written rating, very hot environment, and unplugged.

While SSDs are inferior for long term data persistence if it’s irreplaceable data you should be bring the file system online on a schedule and let it run checksums. If something errors restore from another copy. The magic of digital storage is perfect copies at low cost. The loss of any one copy is fine as long as it has been copied forward elsewhere.

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