Unpowered SSDs slowly lose data • Hacker News Board

Re: Unpowered SSDs slowly lose data

#231

Post by Yokolos » Tue, Nov 25, 2025, 12:52 PM UTC

formerly_proven wrote: post #171

Yokolos wrote: post #17

Earlier quoted context omitted.

Any given TBW/DWPD values are irrelevant for unpowered data retention. Afaik, nobody gives these values in their datasheet and I'm wondering where their numbers are from, because I've never seen anything official. At this point I'd need to be convinced that the manufacturers even know themselves internally, because it's never been mentioned by them and it seems to be outside the intended use cases for SSDs

Example: https://www.ssd.group/wp-content/uploads/2022/07/PM1733-25-S... > Component Design Life 5 years > TBW 14 PB for 7.68 TB drives > Data Retention 3 months And then 2.7.3 explains that this number applies for 40 °C ambient, not the operating/non-operating range (up to 85 °C).

That's literally just the JEDEC spec.

Re: Unpowered SSDs slowly lose data

#232

Post by tensility » Tue, Nov 25, 2025, 12:56 PM UTC

sevensor wrote: post #3

Flash is programmed by increasing the probability that electrons will tunnel onto the floating gate and erased by increasing the probability they will tunnel back off. Those probabilities are never zero. Multiply that by time and the number of cells, and the probability you don’t end up with bit errors gets quite low. The difference between slc and mlc is just that mlc has four different program voltages instead of t…

At the physical device layer (i.e. what a nand controller vendor programs to), a nand flash device that supports ONFI 2 SLC Mode can be configured to use (some of) its blocks in SLC mode rather than MLC/TLC/QLC/etc. This allows one to divide the array into high-reliability versus high-capacity regions.

Re: Unpowered SSDs slowly lose data

#233

Post by kvemkon » Tue, Nov 25, 2025, 1:03 PM UTC

userbinator wrote: post #168

ACCount37 wrote: post #162

Earlier quoted context omitted.

Because no one is willing to pay for SLC. Those QLC NAND chips? Pretty much all of them have an "SLC mode", which treats each cell as 1 bit, and increases both write speeds and reliability massively. But who wants to have 4 times less capacity for the same price?

4 times less capacity but 100x or more endurance or retention at the same price looks like a great deal to me. Alternatively: do you want to have 4x more capacity at 1/100th the reliability? Plenty of people would be willing to pay for SLC mode. There is an unofficial firmware hack that enables it: https://news.ycombinator.com/item?id=40405578 1TB QLC SSDs are But why won't the manufacturers let you choose? The real…

NVMe protocol introduced namespaces. Is it not the feature perfect for users to decide themselves, how to create 2 virtual SSDs with TLC and pseudo-SLC-mode, choosing how much space to sacrifice for pSLC?

Re: Unpowered SSDs slowly lose data

#234

Post by leo_e » Tue, Nov 25, 2025, 1:18 PM UTC

We learned this the hard way with "cold" backups stored in a literal safe.

We treated NVMe drives like digital stone tablets. A year later, we tried to restore a critical snapshot and checksums failed everywhere. We now have a policy to power-cycle our cold storage drives every 6 months just to refresh the charge traps.

It's terrifying how ephemeral "permanent" storage actually is. Tape is annoying to manage, but at least it doesn't leak electrons just sitting on a shelf.

Re: Unpowered SSDs slowly lose data

#235

Post by johncolanduoni » Tue, Nov 25, 2025, 1:35 PM UTC

DeepSeaTortoise wrote: post #209

lxgr wrote: post #193

Earlier quoted context omitted.

Wrong layer. SSDs know which blocks have been written to a lot, have been giving a lot of read errors before etc., and often even have heterogeneous storages (such as a bit of SLC for burst writing next to a bunch of MLC for density). They can spend ECC bits much more efficiently with that information than a file system ever could, which usually sees the storage as a flat, linear array of blocks.

IMO it's exactly the right layer, just like for ECC memory. There's a lot of potential for errors when the storage controller processes and turns the data into analog magic to transmit it. In practice, this is a solved problem, but only until someone makes a mistake, then there will be a lot of trouble debugging it between the manufacturer certainly denying their mistake and people getting caught up on the usual susp…

ECC memory modules don’t do their own very complicated remapping from linear addresses to physical blocks like SSDs do. ECC memory is also oriented toward fixing transient errors, not persistently bad physical blocks.

Re: Unpowered SSDs slowly lose data

#236

Post by kvemkon » Tue, Nov 25, 2025, 1:36 PM UTC

whitepoplar wrote: post #116

fairfeather wrote: post #111

Earlier quoted context omitted.

A full read would do it, but I think the safer recommendation is to just use a small hdd for external storage. Anything else is just dealing with mitigating factors

Thanks! I think you're right about just using an HDD, but for my portable SSD situation, after a full read of all blocks, how long would you leave the drive plugged in for? Does the refresh procedure typically take a while, or would it be completed in roughly the time it would take to read all blocks?

Does the refresh procedure take place at all?

Re: Unpowered SSDs slowly lose data

#237

Post by whitepoplar » Tue, Nov 25, 2025, 1:38 PM UTC

kvemkon wrote: post #236

whitepoplar wrote: post #116

Earlier quoted context omitted.

Thanks! I think you're right about just using an HDD, but for my portable SSD situation, after a full read of all blocks, how long would you leave the drive plugged in for? Does the refresh procedure typically take a while, or would it be completed in roughly the time it would take to read all blocks?

Does the refresh procedure take place at all?

I would hope so.

Re: Unpowered SSDs slowly lose data

#238

Post by formerly_proven » Tue, Nov 25, 2025, 1:44 PM UTC

Yokolos wrote: post #231

formerly_proven wrote: post #171

Earlier quoted context omitted.

Example: https://www.ssd.group/wp-content/uploads/2022/07/PM1733-25-S... > Component Design Life 5 years > TBW 14 PB for 7.68 TB drives > Data Retention 3 months And then 2.7.3 explains that this number applies for 40 °C ambient, not the operating/non-operating range (up to 85 °C).

That's literally just the JEDEC spec.

Point being?

Re: Unpowered SSDs slowly lose data

#239

Post by jollyllama » Tue, Nov 25, 2025, 1:51 PM UTC

Wowfunhappy wrote: post #94

> But, most people don't need to worry about it. [...] You should always have a backup anyway. [...] Backing up your data is the simplest strategy to counteract the limitations of storage media. Having multiple copies of your data on different types of storage ensures that any unexpected incidents protect your data from vanishing forever. This is exactly what the 3-2-1 backup rule talks about: 3 copies of data on at…

Yeah. That part was so out of touch, I have to wonder who they're carrying water for. Most people backup their data? What planet does the author live on?

Re: Unpowered SSDs slowly lose data

#240

Post by rafterydj » Tue, Nov 25, 2025, 1:53 PM UTC

groestl wrote: post #181

A strong believe of mine: there is no storage, only communication. I hold that thought since I first heard of SRAM, and I think it applies to everything, knowledge, technology, societies, our universe in general..

Interesting statement. I suppose you could argue that long term archival storage is communication with a long tailed, sometimes ill-defined window for receiving the message. Few people write books they don't want anyone to read.