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The Reliability of Optical Disks

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Re: The Reliability of Optical Disks

#111

Post by mrjangles »

nayuki wrote: post #74

Great article discussing the benefits of optical discs and the author's own experience of using them! I burned hundreds of discs a decade ago and read them all back perfectly, to my surprise. I strongly agree with the write-once behavior for photos and downloads. HDDs worry me in the long term because even if the platter holding the data is fine, the R/W head, mechanics, and electronics could fail, not to mention tha…

> Why are new formats not forthcoming?

oooh I can answer this one. About 15 years ago I saw a talk from a team at, oxford I think?, that had invented a way to store many terabytes on an ordinary blue ray by adding rotation to the scratches, which can then be read because scratches at different angles polarized the returning light differently.

Anyway, they had a working prototype and everything and the big companies like Panasonic all said "No sorry, everyone is shutting down their optical drive lines. We have determined that the future is internet storage and solid state. No one wants disk no matter how much storage they can hold." And that was that.

Re: The Reliability of Optical Disks

#112

Post by em3rgent0rdr »

NavinF wrote: post #93
em3rgent0rdr wrote: post #78

Could do RAID 4/5/6 with Optical Disks too for additional paranoia. Ideally there should be some machine to go through old backups and upon first detection of an error, then it could regenerate the array from the remaining discs of that array.

That’s the biggest problem with optical disks. With no automation, it’s totally impractical for one person to maintain a full backup of everything they care about. 100TB is like 2000 discs plus parity.

Yeah. Though it is not difficult to build such a machine and similar machines have been around, such as CD Jukebox players and multi-disc burners.

Re: The Reliability of Optical Disks

#113

Post by rasz »

mrjangles wrote: post #111
nayuki wrote: post #74

Great article discussing the benefits of optical discs and the author's own experience of using them! I burned hundreds of discs a decade ago and read them all back perfectly, to my surprise. I strongly agree with the write-once behavior for photos and downloads. HDDs worry me in the long term because even if the platter holding the data is fine, the R/W head, mechanics, and electronics could fail, not to mention tha…

> Why are new formats not forthcoming? oooh I can answer this one. About 15 years ago I saw a talk from a team at, oxford I think?, that had invented a way to store many terabytes on an ordinary blue ray by adding rotation to the scratches, which can then be read because scratches at different angles polarized the returning light differently. Anyway, they had a working prototype and everything and the big companies l…

minidisks use polarization

Re: The Reliability of Optical Disks

#114

Post by xhkkffbf »

rhn_mk1 wrote: post #110
forgotpwd16 wrote: post #107

Earlier quoted context omitted.

>HDDs worry me in the long term Are SSDs any better in that regard?

No, the memory cells lose charge over time. Even one year can cause data loss. Sorry, I don't have the link, but there was someone who tested how latency increased on drives that spent months on the shelf. The explanation was error correction working harder.

You don't need a link. I can corroborate with my own experiences. Flash memory slowly forgets information. One guy told me that he can't unplug is big SSD array because he's afraid to lose a few bits. He might as well call it RAM.

Re: The Reliability of Optical Disks

#115

Post by ghostly_s »

blueflow wrote: post #13
ghostly_s wrote: post #3

I'm a bit skeptical of these conclusions without more detail on the methodology. Does "100% success rate!" mean the author was able to mount the disks and read some files off them? Or did they actually have some method to verify check-sums of every file to identify bitrot?

It matches my experience. Even decades-old CD-ROMs only fail when they are scratched or physically damaged, which you can prevent by keeping them in appropriate cases and always put them back after use.

Again - did you use some method to confirm there was zero bitrot on these discs? Or are you concluding they were still good simply because you were able to get data off them?

Re: The Reliability of Optical Disks

#116

Post by robocat »

neuralRiot wrote: post #70
robocat wrote: post #53

Earlier quoted context omitted.

Blu-ray discs use a red laser, and CD-ROMs use an infrared laser. The drives contain two laser diodes. Skip to 5:50 in https://www.youtube.com/watch?v=h9lbrr04XBQ

Blu-ray uses blue laser (blue-ray!) DVD uses red and CD infrared. Devices compatibles with the 3 mediums have 3 lasers on their optical pickup.

Thanks. I anti-corrected it to red from blue when I found the video, and the statement felt really wrong when I wrote it, but I thought fuck-it - the video link is too good to miss! Lazy me.
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