Disc rot

[Huge]

You're welcome.

[Huge]

[Andy Champ]

Depends on the precise type. Certainly there are papyiri that have lasted 5000 years. And an awful lot of B&W photographs from the end of the 19th century are just fine. On the other hand I have had paper where all the letters fell out after 10 years - must have been acid ink - and early photocopy / laser stuff where the toner welds to the page opposite in a similar timescale.

Andy

[Andy Champ]

Terrabytes are those stored on baked clay tablets :)

Andy

[polygonum]

And petrabytes rock ... ??? :-)

[Huge]

*applause*

[Nightjar]

Most are probably sepia tone, rather than black and white. Sepia tone is fade resistant and will last as long as the paper.

Colin Bignell

[The Natural Philosopher]

or selenium IIRC. I think they used that for astronomical plates.

[Adam Funk]

Easily damaged once you re-open the media for reading, though!

(I think some of the other cave painting sites have had similar problems with humidity from exhaling visitors.)

[Adam Funk]

What do you use for the long-term backups? TBH, part of the reason I've liked DVD-Rs until now (although based on some comments in this thread I'll look at getting DVD+Rs for archiving instead) is that they are read-only. If you delete some files by accident without realizing it and later use rsync (or similar) to update your back-up on another machine, you inadvertently update the mistake!

That's what I thought, thanks.

[The Natural Philosopher]

so rescind teh mistake BEFORE it propagates.

when I looked into this, the answer was simple. Twin big disks (mirrored) and a crappy CPU and rsync.

DVDS simpley aren't big enough and frankly I have issues reading them, even just after they have been burned.

They are not good with long filenames either.

And they are bulky. compared with a 500GB drive.

[Jules Richardson]

Yeah, that's the conclusion I came to as well.

Worse still, I've found DVDs (and CDs) where they'll read fine in some drives, but not in others - so they might appear to be perfectly OK in the hardware that you have now, but then when you want to access them on the hardware that you have in a few years' time, they might be junk.

cheers

Jules

[Andy Champ]

Ah, so before you run rsync you're going to check every photo and make sure that a disc firmware or OS bug hasn't rewritten a sector somewhere crucial and corrupted a file silently?

I run periodic (i.e. probably not often enough) snapshots of my entire system using a backup app. This compresses the whole lot down to not much more than 100 gigs, and reduces the chance that I won't have a backup of that crucial file when I want it. Of course I ought to keep grandfather-father-son copies - but I don't.

Andy

[cl]

I use rsnapshot which is an incremental backup program that uses rsync and hard links to keep incremental backups as far back as you like.

[The Natural Philosopher]

well I dont run windows.

100gis is still too big fora DVD

My home server has data going back around 15years now. Its been transferred between many different disks. Its probably on its 5th by now. Its on its third machine for sure.

None of it is corrupted.

All of it reads.

Whereas the DVD I burned last week immediately was unplayable in parts on tow other machines.

[The Natural Philosopher]

that works, if you must do incrementals.

However very little of my data changes.

And if I am doing e.g. code development I either use a source control system, or manually create a new version with different file names.

[Adam Funk]

If you notice the mistake right away!

Hardware or firmware problems can (rarely) cause such problems on any OS. (I don't run Windows either.)

[The Natural Philosopher]

That's why I have snooper software looking at disk errors.

If they start to rise, I have time to get a new disk in.

Or build a new server if its a MB issue.

[Windmill]

Ten Bluray disks wouldn't be so bulky, but I suspect that writable or rewriteable disks and drives will be as unreliable as early CDs and DVDs. With giant media corporations (the people accused of blocking digital data tapes) doing their best to reduce the reliability.

[Jules Richardson]

Obviously it's dependent on the backup medium and the nature of the compression used, but too many times I've seen subsequent faults render entire compressed archives - or portions thereof - unusable; if you're dealing with uncompressed files then at least there's an increased chance of being able to recover more of the data. Unless the costs really are prohibitive due to the sheer amount of data being stored, I'd always go for uncompressed archives.

Hopefully your backup app at least produces something that's in some kind of standard format (or, slightly worse, but still better than nothing, that the backup format is in the public domain and readily available). I've seen quite a number of ancient backups for where the proprietary software which created them is long-gone :-(

cheers

Jules