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
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