1NIST/GIPWoG - Fred ByersOctober 14, 2004
Reducing Uncertainty
National Institute of Standards and Technology (NIST)
Information Technology LaboratoryInformation Access Division
Fred ByersNIST
100 Bureau Drive, Stop 8940Gaithersburg, MD 20899Email: [email protected]
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Topics
Consumer ViewLife Expectancy Test IssuesAlternatives Benefits
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Manufacturers vs. Headlines
Manufacturers
• Life Expectancy Best Case– ~ 100 – 300 years CD-Rs
– ~ 60 – 100+ years DVD-Rs
Headlines
• Life Expectancy Worst Case– CDs fail in short time frame
– 2 -10 years failure
– “CD Rot”
Consumer View
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Most Commonly Asked Question: How long will my (recordable) disc last?
(CD-R, DVD-R, DVD+R)
Answer: It depends on:• Care and handling
– Physical handling
– Environmental influences
• Initial recording quality– Condition of disc before recording
– Quality of burn (depends on disc and burner)
• Disc construction– Materials
– Manufacturing process
Consumer View
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More Consumer Questions:
• Should I trust my digital content for long-term storage using these discs?
• Which disc should I buy?• What is the minimum number of years I can expect?• Does price make a difference?• Does brand make a difference?• What should I look for in a disc?• Does the recorder make a difference?
These above points are not unique to optical discs.
Consumer View
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What can the user control?
Proper handling– No scratches, etc.
Proper storage– Controlled at recommended storage conditions
• ? Initial recording quality– Good disc – clean, defect free, good recorder
Disc construction – Dependant on manufacturer
Consumer View
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- Relatively New -Long-Term Quality Discs
Archive, or long-term labeled discs are available from some manufacturers
• What does it mean? – How are they different from regular discs?– How many years will they last? Longer LE?– How does manufacturer A compare to manufacturer B?– How are they determined to be longer lasting?
Consumer View
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Disc-Test Proposal
• A test to measure for minimum longevity expectation
• A test that can be performed in a reasonable time for manufacturers
• An indicator to consumers about minimum quality
• A minimum longevity that consumers can use for planning
Consumer View
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Why
• Variation in life expectancy among discs – Quality differences between brands
– Quality differences within brands
• General claims of up to 100 years LE (DVDR)– Actual could be as low as 30 years in normal ambient room conditions
– Some anecdotal stories conflicting with general claims
• User confidence/uncertainty/awareness– Consumer expectations - uncertain or unrealistic
– Planning under uncertainty – refreshing, sampling and migration
Consumer View
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PIE fromMetal-Halide Light
0
500
1000
1500
2000
0 100 200 300 400 500Hours
PI e
rro
r
Aged in high temperature and humidity conditions
DVD-R discs
0
500
1000
1500
2000
0 200 400 600 800
D1
D2
D3
HoursP
I err
or
Aged in Metal-Halide light
DVD-R discs
PIE fromHigh T and RH
DVD-R Accelerated AgingComparison Examples
Consumer View
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Life Expectancy (LE) Test Standards
Existing LE Test Method Standards
• CD-ROM– ISO 18925:2002, AES 28-1997, ANSI/NAPM IT9.21
• CD-R– ISO 18927:2002, AES 38-2000
Consumer View
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LE Testing Issues
• Time duration– Typically one to two years
– Time to market
• Capability– Equipment
– Space
– Expertise
• Cost– Labor
– Contract out
• Existing LE Test Followed?
• No Standard DVD Test
– No Standard LE Test for DVD yet
– NIST is proposing a DVD procedure following the CD Standard
• No Standard “archive quality” test methodology
– NIST proposing a model
LE Issues
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LE - Accelerated Aging Times Stress
Test-SetStressed at (Tinc, RHinc)
Incubation duration
Minimum total time
Specimenquantity
1 80 ºC, 85 % 500 h 2000 h 10
2 80 ºC, 70 % 500 h 2000 h 10
3 80 ºC, 55 % 500 h 2000 h 15
4 70 ºC, 85 % 750 h 3000 h 15
5 60 ºC, 85 % 1000 h 4000 h 30
13,000 h total
80total
LE Issues
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Incubation + Testing TimeNo. of
ChambersIncubation
timeNo. of weeks
Testing time (2 analyzers)
TotalTime
1 13,000 hrs 78 wks 6 wks 84 wks
2 7,000 hrs 42 wks 6 wks 48 wks
3 5,000 hrs 30 wks 6 wks 36 wks
4 4,000 hrs 24 wks 6 wks 30 wks
LE Issues
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Alternatives to the Existing LE Test (to save time and cost)
• Shorten the LE Test– Less expensive
but
– Less accurate
• Initial Error Rate Test– Measures initial quality of data on disc
but
– Does not account for disc degradation rate
– Does not indicate life expectancy
• Target Test - “Archival”, or “Longevity” or “Grade”– Longevity specific, i.e.: minimum number of years expected
– Not a test to determine total disc LE
Alternatives
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Alternatives Continued
• Shorten the LE test– Creates higher uncertainty for total disc LE measurement
But
– Uncertainty level should still be acceptable for a lower limit
• Consider error increase-rate– > x = fail
• Consider initial measurement?– BLER-max > x = not acceptable
– Reflectance < x = not acceptable
Alternatives
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Another ApproachDon’t calculate for LE (T50) but make it a known lower limit.
• Example:
Make LE (or T50) = 50 years = lower limit.
(At storage conditions 20ºC, 50%RH)
Determine from stress tests if disc will perform beyond the lower limit.
Alternatives
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Existing Equation from CD StandardExisting equation from CD-R Standard:T50 = AeH/kTe(B)RH or lnT50 = lnA + H/kT + (B)RH
T50 = Time duration for median disc in a test-set to reach BLER-max (220).A, H and B determines the rate at which median disc reaches maximum allowed errors (220).
Normally we derive A, H and B from test data, then calculate for T50.
Constants:
k
T (Temperature)
RH
Derive from test data:
A
H
B
Calculate:
T50 (Time)
Alternatives
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Alternative Use of Existing EquationUsing T50 = AeH/kTe(B)RH or lnT50 = lnA + H/kT + (B)RH
• Instead of calculating for T50, make T50 known.
• For example: T50 50 years (disc reaches BLER-max of 220 in 50 years at a given T and RH)
• Find A and combined e coefficients (H and B) for T50= 50yrs
Constants:
k
T (Temperature)
RH
T50
Derive from T50= 50:
A
H
B
Do not Calculate T50 :
Make T50 = 50years
Use:
lnT50 = lnA + H/kT+ (B)RH lnT50 = 12.99 at 20ºC, 50%RH
Alternatives
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First Stress Test Set500 hour intervals x 4
0
100
200
300
400
500
600Y
1 2 3 4 5
Rows
80C, 85%RH
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Targeted Time Periods?(“Sunscreen” Approach)
• Can have more than one target or establish only one target.– Total disc LE is unknown (not necessary)
– > 30 yrs
– > 50 yrs
– > 75 yrs
– > 100 yrs
• A test for one targeted minimum longevity time period– 50 year example
– Discs are expected to extrapolate to beyond the lower-limit threshold.
– Error rate increases less than an established maximum acceptability
Alternatives
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What will this do for the Consumer? Consumer Indecision Revisited:
• Should I trust my digital content for long-term storage using these discs? (Properly tested discs, yes)
• Which disc should I buy? (Tested discs)
• What is the minimum number of years that I can expect? (As labeled)
• Will price make a difference? (Maybe)
• Will brand make a difference? (Maybe: quality control consistency)
• What should I look for in a disc? (Label showing that the disc batch has passed the test)
• Does the recorder make a difference? (Maybe, same as before)
Consumer View
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Consumer/Industry Benefits• Consumer
– Consumer uncertainty reduced
– More informed choice for consumer
– Increase consumer confidence
– More realistic consumer expectation
– Consumer purchasing can be based on needs or migration plans
• Industry– Industry-wide standard test
– Self-test or third party
– Time to market
– Testing cost (compared to existing LE testing)
– Pricing (cost recovery for implementing new procedure)
Benefits
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What Is Needed From You, The User
• Define what “archival” means to you or what length of time needed for long-term storage.
• What is the minimum length of time needed for a disc to last to satisfy your requirements?
• What is the ideal length of time?
• Will this make a difference in your purchasing decision?
• Will you look for these “labeled” discs for long-term storage applications instead of other discs?
Consumer View
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Other ideas
• Early warning indicator
• RFID
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Early Warning Indicator
• Could also be called:– Error Alert
– Check Disc
• A warning about error rates that are approaching BLER max or PIE max.– May also consider Burst errors
• Just a light as an indicator or a pop-up window
• Gives the actual number (good for initial error rate)
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Thank you!NIST
Information Access Division
Information Technology LaboratoryDigital Data Preservation
Fred Byers, Oliver Slattery, Jian Zheng
http://www.itl.nist.gov/div895/preservation/
Care and Handling Guide
http://www.itl.nist.gov/div895/carefordisc/
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Second Stress Test Set 500 hour intervals x 4
LE Issues
0
100
200
300
400
500
600Y
1 2 3 4 5
Rows
80C, 70%RH
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Third Stress Test Set 500 hour intervals x 4
LE Issues
0
100
200
300
400
500
600Y
1 2 3 4 5
Rows
80C, 55%RH
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Fourth Stress Test Set 750 hour intervals x 4
LE Issues
0
100
200
300
400
500
600Y
1 2 3 4 5
Rows
70C, 85%RH
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Fifth Stress Test Set 1000 hour intervals x 4
LE Issues
0
100
200
300
400
500
600Y
1 2 3 4 5
Rows
60C, 85%RH