when archiving on DVD, should i make a mirror copy similar to RAID 1?

I would like to archive photos. Hard drive (HD) are unreliable after 3-5 years and are not design for long-term storage. DVDs are much better.

From my research i found that TAIYO YUDEN dvd+r is the best option and should last decades. I would like to delete photos off my hard drive and have them on DVD. I like multiple back ups but would like to eliminate HD to save space. I plan to have a dvds at home and a copy at work, also i'd keep a copy on adrive.com (cheap i-net storage).

so i've made identical dvds and stored them in different places. with time dvds will get bad sectors; most likely in different places. i'd like to combine the images of these old dvds with bad sectors to get one good image. similar to mirroring hds with RAID 1.

i'd like to know if there is a program that would combine 2 or more .iso files that have errors and get one without errors.

any suggestions on better archiving options are appreciated.

kirill_igum

Posted 2011-06-07T18:33:48.060

Reputation: 1 098

Answers

dd_rescue

Automatic merging of backups: If you have two or more damaged copies of a file, cdrom, etc, and run ddrescue on all of them, one at a time, with the same output file, you will probably obtain a complete and error-free file. This is so because the probability of having damaged areas at the same places on different input files is very low. Using the logfile, only the needed blocks are read from the second and successive copies.

the program clones the possibly damaged images. while cloning, it notes bad sectors in a log file. when 2 or more of the cloned images and the log files are combined, the bad sectors are replaced by good sectors.

Note: for compressing files, there is lzip. it is based on lzma but with added rescue features (Lziprecover) it is also works with dd_rescue.

kirill_igum

Posted 2011-06-07T18:33:48.060

Reputation: 1 098

You can also make a majority vote to ensure you get a corrected backup file, ensuring you won't overwrite good bytes with corrupted ones.

– gaborous – 2016-12-28T00:17:32.837

1-1 This is just a link and a copied text. – Max Ried – 2011-06-14T09:56:35.347

1@bot47 in the question, i asked for a program that would combine two or more .iso to get a correct image. dd_rescue is a program and it does exactly what was in the question. it uses logs to do that. what kind of answer should it be than? – kirill_igum – 2011-06-14T16:24:01.630

The best backup/archive policy is 3 copies: 1 primary, 1 backup in case the primary fails, and 1 off-site in case of a fire or such.

Ignacio Vazquez-Abrams

Posted 2011-06-07T18:33:48.060

Reputation: 100 516

The reason why RAID 1 works is because, in the event of a read failure, the other drive is consulted. The drive with "good" data is determined by which one failed to read. If a drive is corrupted in-place (i.e. when not in use) and subsequently read, then conceptually there is an ambiguity over which drive is right.

If I needed to use DVDs, I would do what you're doing and make three (3) copies for each location. That way, if there is a corrupted disk, the corrupt bits can be determined by "majority vote". I don't know of a program that does this, but it wouldn't be hard to write.

I would probably also refresh each site every 5-7 years to avoid relying on aged media. If I were in a position where I was concerned enough to back up my data off-site in three locations, I would take the additional precaution even if the disk vendor says it is not necessary.

Alex Hirzel

Posted 2011-06-07T18:33:48.060

Reputation: 996

I agree with alhirzel here. I have backed up to DVD with what I thought were high quality DVDs before only to find many of them were unreadable only a few years later. Backup and re-backup as often as economically possible. – darkAsPitch – 2011-06-16T05:38:56.557

The best method I've heard for backing up data is the 3-2-1 method. That is: three copies of the data, two media types and one off-site.

uSlackr

Posted 2011-06-07T18:33:48.060

Reputation: 8 755

Best archive medium so far is DVD-RAM, but it's hardly available today. But you should still be able to grab one.

Don't expect normal burnable to last for more than 4 years, if you rely on them as your major backup no longer than 1 year. Keep them dark, dry and non-condensing cool. The problem is the organic dye used in those. DVD-RAM uses anorganic dye, which lasts about 10x long.

HDDs should be the best in price/capacity ratio and from my experience their lasting way longer than organic DVD-Rs.

Best would be tape, dvd-ram or stone plates.

Max Ried

Posted 2011-06-07T18:33:48.060

Reputation: 1 521

"Taiyo Yuden states their Super Cyanine dye is chemically stable for at least 70 years" http://adterrasperaspera.com/blog/2006/10/30/how-to-choose-cddvd-archival-media

– kirill_igum – 2011-06-07T20:05:42.860

Of course they do. Maybe if it's deep frozen. In an Faraday cage. In vacuum. They want to sell it to you. – Max Ried – 2011-06-07T20:09:52.343

Tape is certainly not reliable long term, and is not economically viable and is falling out of use these days. On the other hand, I still have CD-R discs I burned back in 1998 that still work fine today, and DVD+RWs from 2004. – psusi – 2011-06-08T01:30:16.387

So you're lucky. I just moved and had to trash nearly all burnt media. The dye had clearly visible coin-size spots or the data layer was even popping up. – Max Ried – 2011-06-08T07:46:48.370

although it's a fact that dvd-ram will last decades i would think that DVD-R caught up to them. for example Verbatim does not produce them anymore (there are none on the website). instead they have "Archival Grade Gold DVD-R". DVD-Rs are a lot cheaper dvd-ram is 3-4$ vs high quality dvd-rs for .4$ (you can burn 6 copies). i couldn't find more details but high end manufactures like Verbatim claim they have a special die like azo or with metal additives. unless one needs to rewrite dvds, i'd say that high quality dvd+r would be better – kirill_igum – 2011-06-13T18:11:23.483

The best way to ensure long term archival is to use Error Correction Codes (ECC) codes such as Reed-Solomon, but they are complicated and long to calculate. This is way more efficient (in terms of resiliency against data corruption) than using a RAID 1 (duplication) scheme.

For DVDs and other optical mediums such as Blu-Ray, there is the great DVDisaster library with the RS03 scheme. It however runs only on Linux (old versions used to run under Windows, but they lack the RS03 scheme so I advise to use the latest release only).

About the reliability of various optical mediums and brands, scientific studies found that Blu-Rays are overall better than DVDs, you can read more info about it in my other answer here.

gaborous

Posted 2011-06-07T18:33:48.060

Reputation: 1 412