Maybe it's just a precision problem? I calculate the durability from PL(*) columns with the formula: 1-PL(site)-PL(copy)-PL(NRE).
Result: 2-cp is 0.99896562 3-cp is 0.99900049 Both of them are approximates to 99.9% Actually the model result is 99.900%. Maybe the author wants us to ignore the last few zeros lol. On Fri, Aug 28, 2015 at 6:26 PM, Gregory Farnum <[email protected]> wrote: > I haven't looked at the internals of the model, but the PL(site) > you've pointed out is definitely the crux of the issue here. In the > first grouping, it's just looking at the probability of data loss due > to failing disks, and as the copies increase that goes down. In the > second grouping, it's including other factors like the entire data > center getting knocked out. That possibility is greater than losing > data due to three disk failures here, so it's capping the total data > durability. > -Greg > > On Sat, Aug 22, 2015 at 2:38 AM, dahan <[email protected]> wrote: > > Hi, > > I have crosspost this issue here and in github, > > but no response yet. > > > > Any advice? > > > > On Mon, Aug 10, 2015 at 10:21 AM, dahan <[email protected]> wrote: > >> > >> > >> Hi all, I have tried the reliability model: > >> https://github.com/ceph/ceph-tools/tree/master/models/reliability > >> > >> I run the tool with default configuration, and cannot understand the > >> result. > >> > >> ``` > >> storage durability PL(site) PL(copies) PL(NRE) > >> PL(rep) loss/PiB > >> ---------- ---------- ---------- ---------- ---------- > >> ---------- ---------- > >> Disk: Enterprise 99.119% 0.000e+00 0.721457% 0.159744% > >> 0.000e+00 8.812e+12 > >> RADOS: 1 cp 99.279% 0.000e+00 0.721457% 0.000865% > >> 0.000e+00 5.411e+12 > >> RADOS: 2 cp 7-nines 0.000e+00 0.000049% 0.003442% > >> 0.000e+00 9.704e+06 > >> RADOS: 3 cp 11-nines 0.000e+00 5.090e-11 3.541e-09 > >> 0.000e+00 6.655e+02 > >> ``` > >> > >> ``` > >> storage durability PL(site) PL(copies) PL(NRE) > >> PL(rep) loss/PiB > >> ---------- ---------- ---------- ---------- ---------- > >> ---------- ---------- > >> Site (1 PB) 99.900% 0.099950% 0.000e+00 0.000e+00 > >> 0.000e+00 9.995e+11 > >> RADOS: 1-site, 1-cp 99.179% 0.099950% 0.721457% 0.000865% > >> 0.000e+00 1.010e+12 > >> RADOS: 1-site, 2-cp 99.900% 0.099950% 0.000049% 0.003442% > >> 0.000e+00 9.995e+11 > >> RADOS: 1-site, 3-cp 99.900% 0.099950% 5.090e-11 3.541e-09 > >> 0.000e+00 9.995e+11 > >> > >> ``` > >> > >> The two result tables have different trend. In the first table, > durability > >> value is 1 cp < 2 cp < 3 cp. However, the second table results in 1 cp > < 2 > >> cp = 3 cp. > >> > >> The two tables have the same PL(site), PL(copies) , PL(NRE), and > PL(rep). > >> The only difference is PL(site). PL(site) is constant, since number of > site > >> is constant. The trend should be the same. > >> > >> How to explain the result? > >> > >> Anything I missed out? Thanks > >> > > > > > > _______________________________________________ > > ceph-users mailing list > > [email protected] > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > >
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