HOW DVD RECORDERS CASUSE DVD DISCS TO FAIL
UNDERSTANDING THE HEART OF THE PROBLEM...
THE SPIRAL DATA TRACK
Diagrams Below shows the different "Track Format Patterns" for different disc technologies with tracks not-to-scale.
Center Row (below):
Bottom Row (above):
"Comparison disk storage" by Cmglee - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Comparison_disk_storage.svg#mediaviewer/File:Comparison_disk_storage.DATAME
The Spiral Data Track on an Optical Disc serves two functions:
Criteria for a Perfect Recording:
The Library of Congress Optical Disc Longevity Study achieved criteria #4 above -- using DVD industry (insider) consultants, a team of engineers, specialized disc recorders, and only after "culling" the best of the best discs (from 2 brands) -- OVER A 5 YEAR PERIOD.
Since this technical level of accomplishment is beyond the financial and technical means of most businesses and common consumers -- NARA banned recordable DVD discs from being used in "National Archives" - including the Library of Congress -- one month after the "official" results of the Library of Congress Study.
This study asserted that it was "possible" for recordable DVD to retain complete sets of data for 40 years.
On the other hand, NARA says a recordable DVD could fail within 1 year, should be checked every 2 years, and should never be used as an archive medium.
This presents a problem to all those Wal-mart-LIKE" companies "selling video "archive services" -- on "recordable archive DVDs" -- calling them "archive worthy" -- since, as an industry, we "archivist" have ALL KNOWN ALL THIS -- since NARA rejected recordable DVD disc for archive purposes -- way back in 2007.
That these "archive services" and "archive products" were, and are, sold to mostly the poor, to woman, and to minorities -- is subject matter for another discussion -- possibly in a court of law.
I am just the little old messenger!
LONGEVITY: ONLY WITH STRICT RECORDING QUALITY CONTROLS
Animated Spiral: Source: Giphy.com: http://giphy.com/gifs/spiral-viral-JN7rcwL4B9cDm
The spiral above shows the complexity of motion -- thus the complexity of writing data to a "moving target" on a spinning spiral tracks.
"Burning a disc" at slower speeds produces fewer "data errors".
Burning to a disc with larger spacing between the track, produces fewer "data errors".
What is a "data error"? "Good data" recorded "off-track" or "bad data" recorded "on track".
The animation (below) shows another "moving target" problem. If the center of the hole in the disc is "slightly off-center" -- or if the spindle inside the disc recorder is "slightly off-center" -- and IF TRACK IS SPINNING (which it is not in my example) -- even the best recorder produces many data errors!
Animated Spiral: Source: http://giphy.com/gifs/works-pump-spirals-miqh2rTtSksOk
Although this spiral does not spin, it does demonstrate the problem of targeting a specific point on spiral track that is off-center.
Wear and tear on DVD manufacturing equipment tolerances, wear and tear on a DVD player, variations in voltage, friction due to dust and to no lubrication on the drive train, and much more -- can affect the quality of the spin -- on a spiral data track.
For ALL the problems above, DVD recorders -- WERE NEVER STANDARDIZED! Each "DVD recorder manufacture" picked the problems THEY wanted to tackle -- their own way -- producing DVD recordings -- on the brink of failing.
The cheapest DVD discs and the cheapest DVD recorders -- have survived. Using the two, together, is why NARA has revised the "longevity" of DVD recordings -- DOWN -- from 2 to 5 years -- to NOW only 1 year.
NOTE: Burning an M-Disc on an "off-the-shelf" DVD or Blu-ray "recorder" -- WILL create an M-Disc -- full of "data errors"! Placing that same M-Disc on the hot dashboard or seat of a your car -- for a couple hours -- will tell you a lot about "longevity statistics".
LAST BUT ON LEAST:
All "optical discs" are "light sensitive" -- even M-Discs. Photons from random sources -- of random wave lengths -- WILL create "bad data" from "good data" on both the "spiral data track" and even more "bad data" -- between the spiraled track -- of all photo-sensitive discs.
This last "fact-of-light", pushes optical discs, most of which are on the very brink of failure from "data errors" - over the edge -- sometimes in less than a year -- after being burned.
Add to this fact, that DVD "players" are going the way of CD "players" -- due to Netflix-LIKE internet services.
I love my CD and DVD discs, but they are looking more like my VHS tapes and vinyl records -- every day!
Still want your hone movies video archived to DVD?
Unfortunately, mass bombardment of both particles and photons -- is an argument (in quantum physics) against optical discs -- and the equipment needed to play them -- as protection against an EMP or Mass Solar Flare Event.
Truth is, we really do not know "the truth" -- even with Faraday protections!
Bottom line, now you know, why a spiral data track is much easier to read right -- than it is to write right; and why optical discs -- of any kind -- are NOT "archive worthy" -- because "recording techonology" was never "standardized".
DISC/RECORDER PROBLEMS AFFECTING LONGEVITY
The NIST/Loc Study states THE PROBLEM with recordable optical disc as follows:
(quote from study) "There are many formats and speeds of (CD/DVD) discs (for example, 4X, 8X, 16X…) in the market and yet there is no unified standard for the (CD/DVD) drive write strategy. Therefore each (CD/DVD) recorder drive manufacturer develops their own (CD/DVD) drive to satisfy the write/read requirements of recordable CD and DVD discs.
As such, there is no guarantee that the (CD/DVD) recorder used to burn a (CD/DVD) disc is fully compatible with that (CD/DVD) disc.
This can, and often does, lead to very high (CD/DVD) error rates immediately after recording the (CD/DVD) disc..."
RECORDING ERRORS: Laymen can regard a "data error" as a "digital scratch" in the "dye layer" in the disc. Too many "data errors" cause a "data block" to fail -- much like too many scratches on a DVD movie rental disc.
In Layman's terms, there are many types and many brands of recordable discs" to which a Disc Recorder MUST be able to both write and read. Disc Recorder Manufactures were left to their own proprietary method of writing to the "spinning spiral track" and different "dye layer" formulas -- of ALL these discs. To this day, there is NO "uinified standard" for writing data to "all these discs".
In addition, there are "Quality Control Variations" across both the DVD Disc and Disc Recording Industry ( more below). As a results there is great imcompatibility between the many discs and the many disc recorders. These imcompatibilities result in many "data errors" or "recording errors" -- which in turn profoundly empacts "data longevity" on an recordable disc.
DISC/DISC RECORDER INTEGRITY
The electric motor of the disc recorder and the laser arm must be perfectly synchronized with movement in the constantly changing "data write point" on the spinning spiral track of the disc.
For this reason, The NIST/LC Study was very strict is finding data parity errors, out-of-balance jitter, asymmetry from faulty spiral data tracks on optical discs.
DISCS ARE REMOVABLE: "Manufacturing Tolerances" for REMOVABLE DISCS and DISC RECORDERS are much greater than for a disc which is firmly and permanently mounted in the recorder (like a hard drive). Greater tolerances mean greater numbers of "recording errors".
QUALITY CONTROL DRIFTS: Quality control drift can be accounted for in 1) differences between manufactures production methods, and 2) differences due to wear and tear of equipment used to produce billions of discs and millions of disc recorders.
DISC DESIGN PROBLEMS
SPINNING SPIRAL DATA TRACKS
The hole in the a mass produced disc must be precisely centered and seated on the disc recorder hub. An asymetric hole (off-center) will cause "spiral wobble". A "worn" hub inside a disc recorder, has the same effect
Physical variance in spin-speed of the spiral data track causes the data to be writen "off-target" or "off-track".
Wear and tear or loss of lubrication -- in moving parts of the recorder -- can cause the disc recorder to write to the wong position on the spiral track.
Quality control drift in manufacturing or daily wear, the disc will have "wobble" in the spinning spiral track -- to which data is to be written.
RECORDING SPEED: The slower the record speed, the fewer "recording errors. Because there may be very slight "wobble" in many spinning spiral tracks, "recording speed" plays a roll in "disc errors" and thus in "data longevity. A recorder may compensate for "very slight wobble" -- at slower spinning speed -- but loose data integrity at higher speeds..
In the event one or more of any of the above physical factors are less than perfect, massive "recording data errors" would be -- and ARE -- commingled with "good data" and retained in the "dye layer" of the disc.
SIMPLE AGING: Aging creates MORE data errors in the "dye layer". If the disc is already full of "data errors" -- in ALL data blocks -- WHICH IS COMMON (according to the NIST/LoC Study) -- with each block on the brink of failure -- simple aging of the "dye layer" -- 2 to 5 years -- is enough "True-to-Life™" time to cause any one OR MORE of the data blocks to fail.
Eventually, ever componding errors can cause the entire disc to fail -- like a "rental movie DVD" -- with too many scratches.
Bottom line, the result is failure of data blocks -- in 2 to 5 years -- and eventually the disc itself.
In real life -- YOUR RESULTS MAY VARY!
UNDERSTANDING "THE CONTROLS" OF THE NIST/LC STUDY