R: Large discs

[Mazzini Alessandro]

The M kind of dvd supports guarantee over 1000 years of retention, and
resistance to acid/alien invasion/etc

-----Messaggio originale-----
Da: cctalk [mailto:cctalk-bounces at classiccmp.org] Per conto di Paul Koning
via cctalk
Inviato: venerdì 5 gennaio 2018 21:45
A: Warner Losh; General Discussion: On-Topic and Off-Topic Posts
Oggetto: Re: Large discs



> On Jan 5, 2018, at 3:24 PM, Warner Losh via cctalk <cctalk at classiccmp.org>
wrote:
> 
> On Fri, Jan 5, 2018 at 1:13 PM, Fred Cisin via cctalk 
> <cctalk at classiccmp.org
>> wrote:
> 
>> On Fri, 5 Jan 2018, Mazzini Alessandro wrote:
>> 
>>> I'm  not sure I would use SSD for long term "secure" storage, unless 
>>> maybe using enterprise level ones.
>>> Consumer level SSD are, by specifics, guaranteed to retain data for 
>>> 6 months
>>> 
>> 
> The JEDEC spec for Consumer grade SSDs is 1 year unpowered at 30C at 
> end of life.
> The JEDEC spec for Enterprise grade SSDs is 90 days, unpowered at 30C 
> at end of life.

That's curious.  Then again, end of life for enterprise SSDs is many
thousands of write passes over the full disk (or the same amount of writes
to smaller address ranges thanks to remapping).  Under high but not insane
loads that takes 5-7 years.  So presumably the retention while fairly new
(not very worn) is much better.  Still it's surprising to see a number that
small.

> As far as I've seen, all SATA and NVME drive vendors adhere to these 
> specs as a minimum, but there's also a new class of drive for 'cold
storage'
> which has high retention, but low endurance and longer data read times...

I don't know if the "cold storage" SSD stuff is going anywhere.  But in any
case, it seems to aim at high density at the expense of low endurance.  I
don't remember hearing retention discussed at all, higher or unchanged.

Having drives with limited retention seems quite problematic.  And
"unpowered" suggests that leaving the power on would help -- but I don't see
why that would be so.

As for writable DVDs and such, do they have any useful retention specs?  

	paul