Thanks for the clarification, we're good then :-) On 03/07/2014 12:27, Andreas Joachim Peters wrote: > Hi Loic, > as much as I understood for now it should not happen in Jerasure, but it will > happen with the default Vandermonde matrix in the Intel library. The reason > is the way these matrices are constructed. > > But to verify this you have to make millions of iterations not only 1 because > for large (k,m) there many failure scenario (chunk combinations) to test. > > Cheers Andreas. > > ________________________________________ > From: Loic Dachary [[email protected]] > Sent: 03 July 2014 12:22 > To: Andreas Joachim Peters > Cc: Ceph Development > Subject: Checking of Reed-Solomon Vandermonde parameter combinations > > Hi Andreas, > > There are some combinations of K/M parameters for which Reed-Solomon > Vandermonde may not be able to recover from the loss of M chunks. > Reed-Solomon Cauchy does not suffer from this problem. (I'm paraphrasing a > conversation we had in private, feel free to correct me if I'm wrong). > > In the context of Ceph we are interested in a limited range of parameters so > I ran a test with: > > https://github.com/ceph/ceph/blob/master/src/test/erasure-code/ceph_erasure_code_benchmark.cc#L40 > > for k in $(seq 2 50) ; do for m in $(seq 1 $k) ; do echo -n "k=$k m=$m " ; > ./ceph_erasure_code_benchmark --plugin jerasure --parameter > directory=.libs --parameter technique=reed_sol_van --parameter k=$k > --parameter m=$m --erasures $m --iterations 1 --workload decode ; > done ; done > > and it does not throw an error. It basically take a range of parameters > K=2,M=2 up to K=50,M=50 and decode with M erasures for each of them. Should > some of them fail ? > > Cheers > -- > Loïc Dachary, Artisan Logiciel Libre >
-- Loïc Dachary, Artisan Logiciel Libre
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