how good is the data reliability with CD ROM and DVD RAM?

Devin Monnens dmonnens at
Mon Jul 23 08:21:15 CDT 2018

> I have a lot of backup here stored in CDs, and I have recently bought
> an SCSI DVDRAM unit to create new backups in caddies DVD-RAMs (of
> 4.2Gbyte each)

what is your experience?

 I recently disposed of a couple hundred DVD and CD backups I'd made. As
mentioned in a previous comment, it's simply too impractical to store
terabytes of information in 4.7GB segments, plus they take up a LOT of
space. HDDs aren't the most reliable, but this is what I use now for that
reason. I make sure to keep the previous backup in case something happens.
I'll only use optical backups now with the most important data.

Backblaze has some interesting stats regarding HDD reliability (they are a
data center using thousands of drives running constantly):

As noted previously, beyond storage conditions, disc longevity depends on
the types of dyes used in the discs. Gold is supposed to be best. Early on,
they experimented with a wide variety of dye types, and the silver dyes
were least reliable, oxidizing in only about 10 years.

The thing is, no media format is going to last forever. The only really
reliable way of keeping data around is multiple backups and data migration.
Basically, for your really important stuff, you'll want a couple of
backups, stored in different geographical locations (one local, one on
cloud works, too). You'll want to periodically refresh the backups by
migrating the data onto fresh media.

In the preservation business, the ideal is to refresh after the cost of
storage media is 1/2 of the initial investment. So, if you paid $1 a GB for
the initial storage media, you'll want to migrate once the new format is
$0.50 a GB, and then again when it is $0.25 and so on. This way, the total
cost is double what you initially invested.

Of course, while the cost per GB might drop steadily, the total amount on a
particular media format will increase as well, such that the $150 HDD you
bought 5 years ago will have twice the storage for...$150. Definitely open
to other suggestions.

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