Checking of Reed-Solomon Vandermonde parameter combinations

[Loic Dachary <loic@dachary.org>]

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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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