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The Reliability of Optical Disks

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Re: The Reliability of Optical Disks

#41

Post by btrettel »

uniqueuid wrote: post #36
btrettel wrote: post #34

Earlier quoted context omitted.

One thing that keeps me from trying tapes is that they are still magnetic. If there's some sort of local electromagnetic event then I'd prefer to have a backup that can handle that. I keep some backup hard drives in metal boxes, which is probably enough (Faraday cage). However, optical disks can almost certainly survive a major electromagnetic event without special precautions.

Interesting. Is a magnetic event more plausible for you than other types of decay? I'd expect physical damage from something like a flooding to be much more likely than some sort of magnetic interference. But that probably depends on the location you live in!

I don't know how likely some sort of electromagnetic event is. I just figure that if I'm going to diversify my backup strategies then something dissimilar/uncorrelated would probably be a better choice. My data is on magnetic hard drives, SSDs, and optical disks, each of which has different risk profiles.

As wtetzner said, it's unlikely that a single event could cause all of these to fail. An EMP attack might take out my magnetic hard drives and SSDs but leave the optical disks unaffected. I've also had a hard drive fail due to impact damage that likely would not affect a SSD. Flooding is not something I've thought about before, but since my backups are located in different geographical areas, I should be covered there. Etc.

Re: The Reliability of Optical Disks

#42

Post by formerly_proven »

simonebrunozzi wrote: post #35
hlieberman wrote: post #30

If I am looking at a ~100 years timescale for preservation of documents, there are exactly two choices that I would consider. At the hundreds of years timescale, exactly one. Those are, in order: 1. Microfilm/microfiche 2. Ink on 100% cotton paper, or ink on vellum The properties of microfilm have been well studied. It requires no technology other than a magnifying glass to read, has a well over 500 year lifespan in…

How would you "print" your backup on a microfilm?

Lasers, just like normal film prints.

Re: The Reliability of Optical Disks

#43

Post by mjhagen »

bufferoverflow wrote: post #8

I have many degraded CDs and DVDs from 2000-2010. No drive would read them. Most from reputable brands. Most non-RW. All stored in dark places, indoors.

I have a couple CD-Rs (from the early 2000s) that have completely lost their top layer. I suspect the cause is the label sticker that was used. But in any case, it's completely unreadable.

Re: The Reliability of Optical Disks

#44

Post by axiolite »

btrettel wrote: post #34
uniqueuid wrote: post #32

One option that hasn't been mentioned is tape archives. It's not for everyone, but tapes (LTO) do have a lot of technology and infrastructure behind them that is built for longevity. In particular, you can do cost-efficient archives to multiple tapes and store them in safe locations. If (and that's a big if) the base cost of the drive is tolerable. There was recently a wonderful post and discussion on LTO for "normal…

One thing that keeps me from trying tapes is that they are still magnetic. If there's some sort of local electromagnetic event then I'd prefer to have a backup that can handle that. I keep some backup hard drives in metal boxes, which is probably enough (Faraday cage). However, optical disks can almost certainly survive a major electromagnetic event without special precautions.

> local electromagnetic event then I'd prefer to have a backup that can handle that.

First of all, the magnetic gauss needed to flip bits on LTO media is huge. It's not a practical concern unless you're choosing an incredibly inappropriate storage location.

Second, why wouldn't you store your tapes in a case or a vault that is magnetically shielded?

You probably store your discs in cases, instead of insisting they be naturally durable against rough handling and abrasion.

Re: The Reliability of Optical Disks

#45

Post by ndiddy »

uniqueuid wrote: post #32

One option that hasn't been mentioned is tape archives. It's not for everyone, but tapes (LTO) do have a lot of technology and infrastructure behind them that is built for longevity. In particular, you can do cost-efficient archives to multiple tapes and store them in safe locations. If (and that's a big if) the base cost of the drive is tolerable. There was recently a wonderful post and discussion on LTO for "normal…

IMO the biggest problem with tapes is getting data off of them. The LTO standard only has compatibility for 2 generations back (i.e. an LTO-6 drive can read LTO-5 and LTO-4 tapes, but nothing before then). This means that if you have data you want to store for 30 years, you will also need to factor in the difficulty of finding a working tape drive and a computer that can operate it. With optical media, a new Blu-Ray drive can read a CD-R from the 90s so this is less of an issue.

Re: The Reliability of Optical Disks

#46

Post by tablespoon »

simonebrunozzi wrote: post #35
hlieberman wrote: post #30

If I am looking at a ~100 years timescale for preservation of documents, there are exactly two choices that I would consider. At the hundreds of years timescale, exactly one. Those are, in order: 1. Microfilm/microfiche 2. Ink on 100% cotton paper, or ink on vellum The properties of microfilm have been well studied. It requires no technology other than a magnifying glass to read, has a well over 500 year lifespan in…

How would you "print" your backup on a microfilm?

> How would you "print" your backup on a microfilm?

There are services that can do that for you. You send them document images, they send microfilm back. I've never actually done it, but I've considered it, an I had this random service in my bookmarks: https://overnight-scanning.eu/microfilming-service/

Re: The Reliability of Optical Disks

#47

Post by uniqueuid »

ndiddy wrote: post #45
uniqueuid wrote: post #32

One option that hasn't been mentioned is tape archives. It's not for everyone, but tapes (LTO) do have a lot of technology and infrastructure behind them that is built for longevity. In particular, you can do cost-efficient archives to multiple tapes and store them in safe locations. If (and that's a big if) the base cost of the drive is tolerable. There was recently a wonderful post and discussion on LTO for "normal…

IMO the biggest problem with tapes is getting data off of them. The LTO standard only has compatibility for 2 generations back (i.e. an LTO-6 drive can read LTO-5 and LTO-4 tapes, but nothing before then). This means that if you have data you want to store for 30 years, you will also need to factor in the difficulty of finding a working tape drive and a computer that can operate it. With optical media, a new Blu-Ray…

True.

But on the flip side, the LTO spec guarantees that this two-generation backwards compatibility will remain for the forseeable future. As the article mentions, it's possible that optical discs will become unpopular and cease to exist completely.

With tapes, you're in the same boat as a bucket full of institutions to whom archives are VERY important. That's a big plus!

Re: The Reliability of Optical Disks

#48

Post by btrettel »

axiolite wrote: post #44
btrettel wrote: post #34

Earlier quoted context omitted.

One thing that keeps me from trying tapes is that they are still magnetic. If there's some sort of local electromagnetic event then I'd prefer to have a backup that can handle that. I keep some backup hard drives in metal boxes, which is probably enough (Faraday cage). However, optical disks can almost certainly survive a major electromagnetic event without special precautions.

> local electromagnetic event then I'd prefer to have a backup that can handle that. First of all, the magnetic gauss needed to flip bits on LTO media is huge. It's not a practical concern unless you're choosing an incredibly inappropriate storage location. Second, why wouldn't you store your tapes in a case or a vault that is magnetically shielded? You probably store your discs in cases, instead of insisting they be…

> First of all, the magnetic gauss needed to flip bits on LTO media is huge. It's not a practical concern unless you're choosing an incredibly inappropriate storage location.

You're right, it does seem huge: https://superuser.com/a/568367/111650

(Some of the links from this answer are quite interesting.)

The issue is that I don't know (and I suspect it's difficult to know or even classified) whether an EMP attack (the main scenario I'm worried about, which can be quite powerful) would be sufficient to cause damage. I don't believe there is a consensus on this though I'd be glad to be proved wrong here.

> why wouldn't you store your tapes in a case or a vault that is magnetically shielded?

I would; as I said I put some magnetic hard drives in Faraday cages. However, I'm not confident that the Faraday cage would be sufficient. A lot of the discussion online about constructing Faraday cages to protect electronics is speculation. I haven't seen any clear data showing that during an EMP attack magnetic data is protected inside of a Faraday cage, or protected without one.

Re: The Reliability of Optical Disks

#49

Post by axiolite »

btrettel wrote: post #48
axiolite wrote: post #44

Earlier quoted context omitted.

> local electromagnetic event then I'd prefer to have a backup that can handle that. First of all, the magnetic gauss needed to flip bits on LTO media is huge. It's not a practical concern unless you're choosing an incredibly inappropriate storage location. Second, why wouldn't you store your tapes in a case or a vault that is magnetically shielded? You probably store your discs in cases, instead of insisting they be…

> First of all, the magnetic gauss needed to flip bits on LTO media is huge. It's not a practical concern unless you're choosing an incredibly inappropriate storage location. You're right, it does seem huge: https://superuser.com/a/568367/111650 (Some of the links from this answer are quite interesting.) The issue is that I don't know (and I suspect it's difficult to know or even classified) whether an EMP attack (th…

> I'm not confident that the Faraday cage would be sufficient.

Faraday cages are not intended for that purpose.

Magnetic shielding is a well understood concept. What you need is some thickness of ferrous metals.

https://en.wikipedia.org/wiki/Electromagnetic_shielding#Magn...

https://web.archive.org/web/20070327130322/https://advancema...

https://interferencetechnology.com/magnetic-shielding-basics...

It's easy to test the efficacy of magnetic shielding yourself if you have a large, powerful magnet and a CRT monitor handy.

Re: The Reliability of Optical Disks

#50

Post by btrettel »

axiolite wrote: post #49
btrettel wrote: post #48

Earlier quoted context omitted.

> First of all, the magnetic gauss needed to flip bits on LTO media is huge. It's not a practical concern unless you're choosing an incredibly inappropriate storage location. You're right, it does seem huge: https://superuser.com/a/568367/111650 (Some of the links from this answer are quite interesting.) The issue is that I don't know (and I suspect it's difficult to know or even classified) whether an EMP attack (th…

> I'm not confident that the Faraday cage would be sufficient. Faraday cages are not intended for that purpose. Magnetic shielding is a well understood concept. What you need is some thickness of ferrous metals. https://en.wikipedia.org/wiki/Electromagnetic_shielding#Magn... https://web.archive.org/web/20070327130322/https://advancema... https://interferencetechnology.com/magnetic-shielding-basics... It's easy to tes…

Noted, thank you much.
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