Michael wrote:
> On Saturday, 8 March 2025 22:48:29 Greenwich Mean Time Dale wrote:
>> Frank Steinmetzger wrote:
>>> Am Thu, Feb 20, 2025 at 11:40:48PM +0100 schrieb Frank Steinmetzger:
>>>> Another thing to consider: don’t put it into the safe for a year without
>>>> powering it up. As was explained in a previous mail, QLC uses sixteen
>>>> different levels of charge inside one single flash cell. The chance of a
>>>> bit flip increases the longer the SSD is powerless and charge slowly
>>>> (very slowly) dissipates. It’s hard to find exact numbers, and it’s more
>>>> of a statistical question. Could be a research topic for a slow Sunday.
>>>> ;-) Also, don’t you live in a hot area?
>>> I knew I’ve seen this data in the past, but couldn’t remeber where and in
>>> what context. I just stumbled upon the relevant info again.
>>>
>>> If you search for "jedec temperature and data retention" you find this
>>> PDF:
>>> https://www.jedec.org/sites/default/files/Alvin_Cox%20%5BCompatibility%20M
>>> ode%5D_0.pdf
>>>
>>> It contains establised standard values for flash durability. On slide 28
>>> it
>>> says:
>>> Client-class SSDs should retain their data w/o power for 1 year if used
>>> 8 hours/day at 40 °C and kept at or below 30 °C when off.
>>> There is also a table for other temperatures; the time is cut in half for
>>> 5 degrees more.
>>>
>>> Mind you, that PDF is 15 years old, TLS had just been released to the
>>> public one year earlier according to
>>> https://en.wikipedia.org/wiki/Multi-level_cell#Triple-level_cell
>>>
>>> -- Grüße | Greetings | Salut | Qapla’ Please do not share anything
>>> from, with or about me on any social network. Some are so convinced,
>>> they don’t even know anymore of what.
>> That is confusing.  Data should be OK for one year without power but
>> only if powered 8 hours per day.  Me scratches my head.  Maybe it means
>> should be OK for a year without power and not sure what to think about
>> rest. 
> As I understand it these are two different performance requirements, which 
> were stipulated in this proposed standard back in 2010.
>
> The first, "Active Use (power on)", describes the level of performance on a 
> typical client workload and operating environment, 8hrs/day at 40°C.  I don't 
> know if this is controller temperature, NAND flash cell temperature, device 
> sensor temperature, PC case temperature, or room temperature.  The actual 
> standard document would explain this, as well as the method for measuring it.  
> Meanwhile, I note my NVMe SSD's sensor tells me the drive is idling at 45.8°C 
> as I write this.  o_O
>
> The second, "Retention Use (power off)", sets a limit of 1 year @30°C.
>
> The FFR and UBER thresholds apply to *both* of the above.
>

They might should have explained both as two separate things instead of
both in almost one sentence.  The way it sounded to me, it was about the
same thing.


>> I suspect that things have changed a lot in that time frame despite the
>> confusion.  They may have improved things significantly since then. 
> Hmm ... I wouldn't take this to the bank.  Standards are typically formulated 
> following consultation with industry to establish the art of the possible, but 
> without cutting too much slack on manufacturers so as to promote innovation 
> and improvement.  The manufacturers seek to minimise overall costs, while 
> keeping their head above the thresholds stated in the standard.  So there's a 
> tension right there, which hopefully delivers innovation and ideally lowers 
> costs over time - but it does not necessarily improve performance.  Check how 
> quality of USB flash drives has gone south over the years, following the 
> trajectory of their price.
>
> The move from SLC to QLC has been effective in reducing costs, but at some 
> point the limits of physics will constrain performance.  It would be 
> interesting to dig out the latest JEDEC standard and compare thresholds to see 
> how they may have improved with more modern manufacturing methods.
>

I suspect SSD for m.2, 2.5" and such are still advancing as far as tech
goes.  USB stuff is likely falling off, except maybe for the really
large USB sticks and some major makers who still value quality. 


>> Still, if the one year part, less the other part, is accurate then but
>> better now, then my powering up even once a month should be OK.  I only
>> need to worry about if something happens to me and no one touches it for
>> many months, a year or longer. 
> Given the temperature of the device would probably be below 30°C for at least 
> half of the year in day time and most nights, I would think your data will be 
> fine.  :-)
>
> I have a 11 year old Toshiba OCZ SSD, which gave me a scare a week ago.  It 
> reported an I/O error, dmesg showed it being inaccessible - I can't remember 
> the exact error.  I thought it was game up with this drive, but surprisingly 
> following my reseating the SATA cable and a reboot later it has worked without 
> further complaints.  With reports of OCZ drives failing at an alarming rate 
> more than a decade ago, I am happy it has lasted this long.


I suspect it is safer than on a USB.  I believe that the old spinning
rust is likely the most durable long term storage without powering up
during storage.  I once hooked up a bunch of old IDE drives that hadn't
had power to them in years.  I went poking around and all the data was
still there.  It had some old videos, pictures, text files and other
stuff.  They all appeared fine to me.  Those drives sat in a out
building with no climate control at all.  Some were sitting on a shelf
bare, no static bag or anything.  They stored just fine.  Heck, I was
worried about the circuit boards more than anything.  Still, they worked. 

Dale

:-)  :-)