Large discs

[Paul Koning]

> 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