Hello Loic, You ask previously: In other words, is there a place where one could set things like "disk fail % of the time" and "network is X Gb/s" and "repairing a disk failure requires disk require reading B bytes from M disks" ? As far as I understand, such factors cannot be expressed with a single formula and this is why a Markov model is useful. I think we need to run simulations to have a more precise estimation of the reliability of an erasure coded system. Markov models are not as flexible as you may think. Besides, solving equations when the number of components that may fail is large makes the problem not trivial. Maybe standard simulation is enough. As observed by Greenan in his thesis, standard simulations have problems with rare events which may not be observed during simulation time. I don't know if we should care about rare events for comparing methods.. Greenan released the software used for his thesis. It is completely developed in Python. http://www.kaymgee.com/Kevin_Greenan/Software.html I found Greenan tool while trying to validate the results of ceph-tool and the numbers are completely different: For instance: Parameters for ceph tool: Disk type consumer, FIT1=2167, FIT2=2167 Size: 2000GiB RAID-6 Replace 0h Rebuild 6000MiB/s Volumes:8 NRE model: ignore Period: 10 years (I used this numbers to compared with model 2DFT.disk.model of Greenan tool) Parameters for Greenan HFRS tool python mm_solve.py -m 2DFT.disk.model -M Results CEPH: storage durability PL(site) PL(copies) PL(NRE) PL(rep) loss/PiB ---------- ---------- ---------- ---------- ---------- ---------- ---------- RAID-6: 6+2 11-nines 0.000e+00 1.318e-12 0.000e+00 0.000e+00 9.887e+02 HRFS: Analytic MTTDL: 4.06111903031e+12 ********************* Analytic prob. of failure: 2.15660e-08 ********************* Could you check if the parameters for ceph are correct and equivalent to HRFS model?Do you think it has sense to include Greenan tool. Greenan has a number of models including nonMDS codes. I am not sure yet how we can describe the LRC code in this platform but it might be possible. koleosfuscus ________________________________________________________________ "My reply is: the software has no known bugs, therefore it has not been updated." Wietse Venema -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
