[Beowulf] Re: Interesting

Lux, Jim (337C) james.p.lux at jpl.nasa.gov
Fri Oct 29 10:49:16 EDT 2010




On 10/29/10 6:50 AM, "Ellis H. Wilson III" <ellis at runnersroll.com> wrote:

> Interestingly, I found "Keeping Bits Safe: How Hard Can It Be?" by David
> Rosenthal in the November Communications of the ACM just released.
> 
> It does discuss data retention at the centuries level, but unfortunately
> does not consider the moon-based strategy proposed by Rob.  Nonetheless
> is a good read for any out there who are now interested in this area.
> However, I do wish flash (or any technology besides normal 3.5in hard
> drives) was considered.  I would expect dormant flash-based technology
> to last quite a while at controlled temperatures.
> 


Flash memory probably has a life time of around 10 years (at reasonable
temperatures). The data is stored as charge on capacitors, and the
capacitors aren't perfect.

Errors tend to be transient.  That is, you read a page again and it reads ok
the second time. (That is, it's not like DRAM, where a bit flips and stays
flipped, so word level ECC works quite well)

So, if you want your flash to hold forever, you'll have to periodically
rewrite it. Say you rewrote every year, you'd get 10,000-100,000 years
before you "wore out" the flash.

There are other aging effects: diffusion of metal ions, etc.  You'd want to
keep your flash cold, (but not too cold, or it will break... No liquid
nitrogen)

I think your best bet is real CDs... That is, the mechanically stamped
variety. They're dense, and nothing beats a mechanical change.  You can
still read Jacquard punch cards from the early 19th century  (in fact, I was
reading an article recently about there being a dearth of loom programmers..
So when your job at the buggy whip factory finally goes away...)

Some sort of photographic technique would also have good archival properties
(e.g. Silver clumps). There are lots of photographic negatives 100 years old
around with little or no degradation.  And it's denser than ink on paper.
100 lines/mm is an easy resolution to get.

Or, how about something like the UNICON aka "terabit memory" (TBM) from
Illiac IV days. It's a stable polyester base with a thin film of rhodium
that was ablated by a laser making 3 micron holes to write the bits.  $3.5M
to store a terabit in 1975.


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