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Availability Distributions |
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Availability Distributions |
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Availability Distributions
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Availability Distributions |
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Availability Distributions |
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This paragraph provides formulas used in calculation of an availability of a single RBD block.
In general, unavailability UA is calculated using the following equation:
UA = MCTeq / (MTBFeq + MCTeq),
where MCTeq is equivalent maintenance corrective time and
MTBFeq is equivalent MTBF.
MTBFeq and MCTeq are calculated differently for each failure and repair times distribution type - see tables below.
Equivalent MTBF calculation for different failure time distributions:
Distribution |
Equivalent MTBF |
Parameters |
|---|---|---|
Exponential |
MTBF |
|
Weibull |
a*Γ((b+1)/2), where Γ is gamma function |
a > 0; (scale) b > 0 (shape) |
Normal |
μ |
- < μ <; σ > 0 |
Log normal |
e(μ+σ*σ/2) |
- < μ <; σ > 0 |
Erlang |
λ*κ |
λ > 0; κ - positive integer |
Time-independent |
0 |
0 Ur 1 |
Constant |
Τ0 |
Τ0>0 |
Uniform |
(a+b)/2 |
0 a < b |
Equivalent MCT calculation for different repair time distributions:
Distribution |
Equivalent MCT |
Parameters |
|---|---|---|
Exponential |
MCT |
MCT |
Weibull |
a*Γ((b+1)/2), where Γ is gamma function |
a > 0; b > 0 |
Normal |
μ |
- < μ <; σ > 0 |
Log normal |
e(μ+σ*σ/2) |
- < μ <; σ > 0 |
Erlang |
λ*κ |
λ > 0; κ - positive integer |
Time-independent |
0 |
0 Ur 1 |
Constant |
Τ0 |
Τ0>0 |
Uniform |
(a+b)/2 |
0 a < b |
