

How Long Do CDs Last? It Depends, But Definitely Not Forever - jedberg
http://www.npr.org/blogs/alltechconsidered/2014/08/18/340716269/how-long-do-cds-last-it-depends-but-definitely-not-forever

======
gmisra
Back in the day (1999) I wrote a data processing and archiving pipeline for a
research satellite, and I was surprised to discover the specificity of their
data archival requirements. Off the top of my head, these were decision
points: * Pretty much only used "gold" CDs, rated for longer storage. * CD
write speed was restricted - higher write speeds caused more write failures *
The total data payload was regulated (~600 MB I think), and one of the reasons
why was because of the physical impact of human handling on the outermost
areas of the disc. * Storage temperature was also regulated

But ultimately, the two main data storage strategies employed were: * Physical
redundancy - six copies of everything, mailed out to six physically separate
facilities every week. * No archiving "forever" \- Archived data was
(theoretically) to be restored to contemporary storage technology whenever
there was a significant step change in storage technology. At the time,
another member of the lab was working on restoring old Voyager data feeds,
although I have no awareness of how common this actually was.

~~~
jacquesm
There is something funny about how pirated movies and music are probably the
most resilient data available and how irreplaceable data like the one that you
reference is the most vulnerable.

Maybe we could set up a scheme where a few megabytes of precious data are
appended to torrents of movies and mp3s for extremely resilient back-ups?

~~~
theandrewbailey
The story mentioned that data was being transferred to servers. Maybe
archivists could tell the internet to download everything?

------
bane
I have a collection of old burned CDs. All, somewhere between 8-13 years old.
Recently I went through and either copied the data to an external drive or
tossed 'em. I was able to get all the data off of probably more than 80%. But
there were a few that I couldn't get anything off. So I'd say maybe 10 years
for burned disks.

My pressed disks (store bought albums and old video games from the same
vintage) seem to be 100% okay unless there's scratches on them.

~~~
tjr
I have been told that is the difference between "duplicating" CDs and
"replicating" CDs, with the latter typically done when making large quantities
of copies.

This article mentions it somewhat:

[http://www.pcworld.com/article/124312/article.html](http://www.pcworld.com/article/124312/article.html)

but I imagine a better article is out there.

------
kqr2
The manufacturer claims these discs will last 1000 years:

[http://www.mdisc.com/what-is-mdisc/](http://www.mdisc.com/what-is-mdisc/)

~~~
ScottBurson
I'm curious about these too. Haven't tried them yet. Has anyone here? (Not
that you would know, yet, how long they last.)

------
zokier
Digital data is best suited for constant replication instead of long term
"cold" archival. 400,000 CDs is just 320TB of data, perfectly reasonable
amount to keep on live hard drives these days. And once you are handling files
instead of physical discs then you can just keep changing the underlying HW as
tech marches on. With checksumming and redundancy, it seems almost impossible
to have bitrot eating data.

------
chiph
I recently ripped all my CDs to WAV files (got tired of the space all those
physical discs were taking up). 800+ CDs, some of which dated back to the dawn
of the digital music era in 1983. Some of them (music from Eurythmics, Dire
Straits, Pink Floyd) required several passes to get a clean copy, but I was
able to copy them all.

In my case, I always kept them in their jewel boxes, which were stored
vertically, much like you'd store an LP. For most of their life they were kept
indoors, but they also spent about 3 years in an unheated storage unit.

The fun part was finding adapters for the few 8 cm CD singles I had, so they'd
play in a modern slot-loading drive.

~~~
ZoFreX
> Some of them (music from Eurythmics, Dire Straits, Pink Floyd) required
> several passes to get a clean copy, but I was able to copy them all.

Did you use something like Exact Audio Copy? It has options to automatically
try try and try again if it reads a bad sector, which really reduces the
amount of (human) time required to rip a disc.

~~~
chiph
I did. I noticed those discs because they took a lot longer.

------
mark-r
Since the main problem seems to be oxidation, I'm surprised nobody recommends
putting them in a sealed cabinet and flushing with compressed nitrogen. Seems
easy and cheap.

------
blueskin_
All you really need to keep data forever is RAID (10 is nice, 1 is the
minimum; for more resiliency, you can mirror the entire array a couple of
times too) with a load of hot spares, perhaps with the copies stored at 4 or
more sites (2+ continents). Radiation shield the lot to reduce bit flips, and
if one occurs, you have a background read process that catches them and uses a
simple quorum to determine the correct value; some form of ECC could also be
built into either the file format or the filesystem itself. As more storage is
needed and/or the distro they are using updates a major version, build a new
system in parallel, replicate first, test, then remove the old one once it's
all verified as good.

An interesting article about the National Archives at Kew:
[http://www.theregister.co.uk/2013/12/11/feature_geeks_guide_...](http://www.theregister.co.uk/2013/12/11/feature_geeks_guide_uk_national_archive/)

------
dm2
Cloud storage would work best, stored at multiple data-centers for extra
redundancy, stored with multiple cloud services to be extra cautious.

Gold CDs claim to last 300 years and are not too expensive:
[http://www.amazon.com/Kodak-Gold-Preservation-Write-Once-
CD-...](http://www.amazon.com/Kodak-Gold-Preservation-Write-Once-
CD-R/dp/B001DC9UFU/)

Here are 50 DVDs for $14 that are suppose to last 50-100 years:
[http://www.amazon.com/Verbatim-DataLifePlus-Printable-
Record...](http://www.amazon.com/Verbatim-DataLifePlus-Printable-
Recordable-95078/dp/B0007M0VXW/)

The 200,000 CDs at the Library of Congress could be backed up on a RAID-1 NAS,
but partnering with a cloud storage service might still be a better idea, plus
it would allow people to download some of the data if the author allows it.

------
ChuckMcM
One of the variables are aluminum vs gold on the reflective surface. I've yet
to have a gold one come back unreadable or corrupted but have a number of
aluminum ones that have.

Compact disc owners have noted 'black crud' as a failure mode, where the
tendrils of black oxide begin to develop on the disk surface between the
layers. My original Cars CD had that happen to it and it was fascinating, it
seemed to have started from a defect on the back of the disk which was not
noticeable until black stuff started growing there.

------
devonkim
I remember looking for a good DVD+R brand when I was backing up my CDs to FLAC
for years and everyone had settled with Taiyo Yuden by all the various
audiophile and archiving obsessed people I could find online. I haven't had a
problem with the DVDs I've burned 10+ years ago now (I checked recently, I
read 30 without a hitch before I was satisfied), but now I'm wondering if
anything has changed since that time.

------
jedberg
When I was in college (mid 90s) it cost about $1 per blank CD. They were rated
at "10 years". However, you could pick up a gold blank for about $5 each, and
those were rated at "100 years". I wonder how accurate that was. I don't have
ready access to either one, sadly.

~~~
kalleboo
I spent this summer ripping my stack of about 100 backup CD-Rs/DVD-Rs dating
back to 1997?99? to store on Glacier instead. They were just lying in stacks
on CD spindles, pretty much the worst kind of storage possible. The majority
copied fine. 2-3 failed with visible damage. 2-3 failed with no visible
damage.

While most of the discs were the cheapest ones teenaged me could get his hands
on, 2 of them were Kodak Gold CD-Rs. One of those was one that failed...

There really is no knowing.

------
Havoc
Half as long as you think they will. No exceptions.

