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ARCHIVES-NRA  July 2011

ARCHIVES-NRA July 2011

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Subject:

Re: Storage of digital formats

From:

Kevin Ashley <[log in to unmask]>

Reply-To:

Kevin Ashley <[log in to unmask]>

Date:

Wed, 13 Jul 2011 18:16:37 +0100

Content-Type:

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Mark Forrest wrote:
> Does anyone have a checklist of ideal storage conditions for different
> digital formats - CDs, different types of floppy disc, external hard drives,
> etc.
> 
>

I've been debating whether to respond on this, but in the light of your
own later followup, as well as other responses, I think I ought to. I think
it's worth recognising that there's a world of difference between ideal
storage conditions, acceptable storage conditions and risky ones. But one
also needs to ask why this material is there and for how long.

The TNA guidance that someone pointed to is a reasonable summary of
the ideal requirements. It captures all of the essential information
in the many parts of BS 4783 (which itself is strongly related to
the ISO series that Stephen Gray referred to, so far as I know.)

When I've given training courses for archivists and records managers in
the past, I've started with that information about ideal conditions. Most
of us can't afford to create storage environments with such ideal conditions,
though. It then becomes useful to know what the effect is of being removed
from the ideal. Luckily there's a fair amount of knowledge about that,
for paper as well as digital media. So, to your next point:

> Our film and sound archive seems to have been used as the default option, but
> I'm not sjure if this is really necessary and wonder if storage in general
> strongrooms or unreglated secure rooms is likely to cause long term damage
>

There are a number of ways in which non-ideal conditions affect digital media.
By far the worst are conditions where temperature and/or humidity undergo
significant rapid change on a regular basis. Continuous storage at a temperature
that is somewhat higher than ideal is probably safer than storage in a room
where temperature is usually within ideal limits but undergos fluctuations
of over 10 degrees in under an hour on a regular basis, for instance.

Very low humidity and/or significantly higher temperatures are also damaging.
Humidity high enough to cause condensation also isn't good. But very low
temperatures aren't a risk for most media - indeed some studies have shown that
storage at typical refrigerator temperatures (about 4C) extends the life of
many digital media.

Whichever you choose, note also the part of the TNA guidance about
acclimatisation. Storage temperatures are not operating temperatures; it's
often ideal to allow media to undergo 24 hours of adjustment before trying to
use it after long-term storage. (The same is true when bringing it in from
an uncontrolled environment.)

One other risk that's sometimes forgotten is from pollutants in the atmosphere.
Volatile chemicals and hydrocarbons can cause significant damage to tape, CD
and disk surfaces. So, don't use freshly-painted rooms and avoid air intakes
that are close to streets full of heavy traffic if possible. If you can't avoid
this, just accept that the predicted lifetime of your media is being reduced
by some percentage.

But even assuming you have some ideal storage conditions, you must think
why you are planning to store these things for extended periods of time.
No one should be planning long-term storage for floppy disks, for instance;
they should be planning to copy the contents to something more durable in
the short term. What conditions the floppies are stored in the interim
probably won't matter that much.

You should be checking the contents regularly for readability - ideally
every six months (again, the TNA guidance covers this.) I think that
you'll discover problems with this in timeframes of a few years with
many types of media. CD and DVD, as widespread consumer formats, are
likely to be supported by hardware and software longer than floppy disks,
for instance. But I would not trust hard disks in storage for longer than
3 years if they are relatively recent. (Oddly enough older drives are likely
to last longer; they weren't being manufactured to a price point quite as
much as more modern portable drives.)

So, don't store your media somewhere where the fluctuations are great,
but beyond that don't worry. Worry more that you should be copying regularly
to something else - even as simple disk images, without worrying about
metadata and file format issues which you mention.

Hope this is of some help.

-- 
Kevin Ashley. Director, Digital Curation Centre         http://www.dcc.ac.uk/
E: [log in to unmask]   @kevingashley      http://slideshare.net/kevinashley
T: +44 131 651 3823    P: DCC, Appleton Tower, Crichton St, Edinburgh EH8 9LE
M: +44 7817 402 498    DCC Helpdesk: +44 131 651 1239

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