What media should I use for long term archives?

Long term archives, archives destined to last, say longer than 10 or 20 years, need special attention, or they're actually likely to fail for one of two reasons:

• Media deterioration: whatever you used for your backup slowly degrades over time so that when you finally get around to needing something from the archive you can't read it any more.

• Technology obsolescence: the equipment we might want to use to read the archives might no longer exist in any conveniently accessible way.

(There's actually a third problem, software obsolescence. Who's to say that the file formats we save as today will be readable in the future? What if there's no reader for Word documents, AVI video or MP3 audio? This too could happen, but it's not something I'll deal with in this article.)

Deterioration has gotten a lot of press in recent years. For example we've heard of old Hollywood movies stored in film canisters falling apart due to chemical reactions, and that archivists are scrambling to save as many of these historical gems as possible.

The same applies to any media you might archive your data to. Floppies, CDs, even hard disks will deteriorate over time.

The million dollar question is how long will each of those last?

And of course there's no specific answer. There are too many variables at play: the quality of the media, the environment that the media is kept in long term, the quality of the device used to create the backups, and so on.

I actually became concerned at some reports that CDs, for example, start to suffer serious degradation after anywhere from 1 to 5 years. I panicked and started to worry about my older archives, dating back 15 years. I began to copy them to a hard drive and not one failed. All my data was still intact.

There are mixed messages about what media types last longest, but my personal rule of thumb is that CDs last longer than floppies, and hard drives last longer than CDs. Each probably by an order of magnitude.

But that brings us to the second problem.

What do you do when the backup media you used is no longer supported by current hardware? I have had, at various times, 7-track tape (think old 1950's computers in the movies), punched cards, and small tape cartridges as my "archives". I have no way to read or use any of those today. Floppy disks are slowly disappearing. There's a lot of information out there stored on "zip drives" - though I haven't seen a reader for those in years.

Will CD's be around forever? That seems unlikely, but the question once again isn't as much if they'll become obsolete, as when.

And what they'll be replaced by.

A lot can change in 10 or 20 years.

So, what do I do?

Well, to start with, some time ago when it became clear that floppy disks were heading into history I copied all my backup floppies on to CD-ROMs.

Next, I make sure to purchase brand-name media. I'm partial to Memorex and TDK for CDs and DVDs myself, but other name brands, including the ones you mention, should do equally well. There are so called premium "archival" CD media, and I don't really have a good read on whether they're cost effective or not.

I still burn backups to CD-ROM (and occasionally DVD, though I still have less faith in the reliability thereof). However, I've also begun a process of copying my oldest CDs to hard disk. Those 15-year old CDs I mentioned? I still have them, but they've also been copied onto an external hard drive, which is itself mirrored to a second drive.

My oldest archival CD is now only 8 years old, and over time I plan to catch up and make that more like 5.

Yes, I copy to hard drives. My plan is for my "next generation" archival backup to be multi-gigabyte hard drives. These are drives that I've placed in external USB enclosures - here I'm betting that while the internal architecture is slowly changing (from IDE/PATA to SATA) external interfaces such as USB will probably be around longer, at least in a backwards-compatible way. So in 10 or 20 years even though what's inside the USB enclosure might then be considered incredibly ancient technology, there'll still be a USB socket to plug it into somewhere and have it work. (And if it still matters, I can then copy whatever I have to whatever would then be considered appropriate storage.)

I think the bets are safer there than on specific media (like CDs or perhaps even DVDs), or internal interfaces such as IDE and SATA.

And once again, I'm trying to make sure to get good quality drives for this project.

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If there's any lesson to be learned about archiving digital data it's that it's not as simple as one might believe. If you truly plan to keep things for a long time, a plan to migrate digital data from older to newer media and devices (and perhaps even formats) seems the only pragmatic solution.