[volunteergrid2-l] Why high availability is crucial

[Shawn Willden]

On Sat, Jan 15, 2011 at 6:20 PM, Billy Earney <billy.earney at gmail.com>wrote:

> using the stats you provide:
>
> 20 servers: 35.8%
> 19 servers: 73.6%
> 18 servers: 92.5%
> 17 servers: 98.4%
> 16 servers: 99.7%
> 15 servers: 99.9%
>
> there's not much difference between 15 and 16.  how about 8/16/16?  Or is
> an uneven number beneficial?
>

There's nothing special about odd numbers.  The above numbers give you a
sense of what write availability should be for different values of H out of
20 servers with 95% availability.

Consider that plus the following table, which gives you the probability of
single-file loss and the expansion factor for different encoding parameter
choices, and you should be able to pick parameters that fit your needs.

The first column is the encoding parameters K/H, the second is the
single-file probability of loss, the third is the expansion factor.  The
Tahoe default line is marked.

1/5 3.1E-07 5.00
2/5 3.0E-05 2.50

1/6 1.6E-08 6.00
2/6 1.8E-06 3.00
3/6 8.6E-05 2.00

1/7 7.8E-10 7.00
2/7 1.0E-07 3.50
3/7 6.0E-06 2.33 <=== Tahoe default (enforced by happiness)
4/7 1.9E-04 1.75

2/8 6.0E-09 4.00
3/8 4.0E-07 2.67
4/8 1.5E-05 2.00
5/8 3.7E-04 1.60

2/9 3.4E-10 4.50
3/9 2.6E-08 3.00
4/9 1.2E-06 2.25
5/9 3.3E-05 1.80
6/9 6.4E-04 1.50

2/10 1.9E-11 5.00
3/10 1.6E-09 3.33 <=== Tahoe default (if enough servers)
4/10 8.2E-08 2.50
5/10 2.8E-06 2.00
6/10 6.4E-05 1.67

2/11 1.0E-12 5.50
3/11 9.8E-11 3.67
4/11 5.6E-09 2.75
5/11 2.2E-07 2.20
6/11 5.8E-06 1.83
7/11 1.1E-04 1.57

3/12 5.9E-12 4.00
4/12 3.7E-10 3.00
5/12 1.6E-08 2.40
6/12 4.9E-07 2.00
7/12 1.1E-05 1.71
8/12 1.8E-04 1.50

3/13 3.5E-13 4.33
4/13 2.4E-11 3.25
5/13 1.2E-09 2.60
6/13 4.0E-08 2.17
7/13 1.0E-06 1.86
8/13 2.0E-05 1.62
9/13 2.9E-04 1.44

3/14 2.0E-14 4.67
4/14 1.5E-12 3.50
5/14 8.1E-11 2.80
6/14 3.1E-09 2.33
7/14 8.9E-08 2.00
8/14 2.0E-06 1.75
9/14 3.3E-05 1.56
10/14 4.3E-04 1.40

3/15 1.2E-15 5.00
4/15 9.6E-14 3.75
5/15 5.5E-12 3.00
6/15 2.3E-10 2.50
7/15 7.4E-09 2.14
8/15 1.8E-07 1.88
9/15 3.5E-06 1.67
10/15 5.3E-05 1.50
11/15 6.1E-04 1.36

4/16 5.9E-15 4.00
5/16 3.7E-13 3.20
6/16 1.7E-11 2.67
7/16 5.9E-10 2.29
8/16 1.6E-08 2.00
9/16 3.5E-07 1.78
10/16 6.0E-06 1.60
11/16 8.1E-05 1.45
12/16 8.6E-04 1.33

4/17 3.6E-16 4.25
5/17 2.4E-14 3.40
6/17 1.2E-12 2.83
7/17 4.6E-11 2.43
8/17 1.4E-09 2.12
9/17 3.3E-08 1.89
10/17 6.3E-07 1.70
11/17 9.7E-06 1.55
12/17 1.2E-04 1.42

4/18 2.2E-17 4.50
5/18 1.5E-15 3.60
6/18 8.2E-14 3.00
7/18 3.4E-12 2.57
8/18 1.1E-10 2.25
9/18 2.9E-09 2.00
10/18 6.3E-08 1.80
11/18 1.1E-06 1.64
12/18 1.5E-05 1.50
13/18 1.7E-04 1.38

4/19 1.3E-18 4.75
5/19 9.8E-17 3.80
6/19 5.6E-15 3.17
7/19 2.5E-13 2.71
8/19 8.8E-12 2.38
9/19 2.5E-10 2.11
10/19 5.9E-09 1.90
11/19 1.1E-07 1.73
12/19 1.8E-06 1.58
13/19 2.3E-05 1.46
14/19 2.4E-04 1.36

5/20 6.1E-18 4.00
6/20 3.7E-16 3.33
7/20 1.8E-14 2.86
8/20 6.8E-13 2.50
9/20 2.1E-11 2.22
10/20 5.4E-10 2.00
11/20 1.1E-08 1.82
12/20 2.0E-07 1.67
13/20 2.9E-06 1.54
14/20 3.4E-05 1.43
15/20 3.3E-04 1.33

-- 
Shawn
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