From mboxrd@z Thu Jan 1 00:00:00 1970 From: Loic Dachary Subject: Checking of Reed-Solomon Vandermonde parameter combinations Date: Thu, 03 Jul 2014 12:22:00 +0200 Message-ID: <53B52EC8.5030708@dachary.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="Taib204a63BJxlHUfgl8PmfcRKdmWLiNt" Return-path: Received: from mail2.dachary.org ([91.121.57.175]:36704 "EHLO smtp.dmail.dachary.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1758548AbaGCKWH (ORCPT ); Thu, 3 Jul 2014 06:22:07 -0400 Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Andreas-Joachim Peters Cc: Ceph Development This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --Taib204a63BJxlHUfgl8PmfcRKdmWLiNt Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Hi Andreas, There are some combinations of K/M parameters for which Reed-Solomon Vand= ermonde may not be able to recover from the loss of M chunks. Reed-Solomo= n Cauchy does not suffer from this problem. (I'm paraphrasing a conversat= ion 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_erasu= re_code_benchmark.cc#L40 for k in $(seq 2 50) ; do for m in $(seq 1 $k) ; do echo -n "k=3D$k m=3D$= m " ; ./ceph_erasure_code_benchmark --plugin jerasure --paramet= er directory=3D.libs --parameter technique=3Dreed_sol_van --par= ameter k=3D$k --parameter m=3D$m --erasures $m --iterations 1 -= -workload decode ; done ; done and it does not throw an error. It basically take a range of parameters K= =3D2,M=3D2 up to K=3D50,M=3D50 and decode with M erasures for each of the= m. Should some of them fail ? Cheers --=20 Lo=EFc Dachary, Artisan Logiciel Libre --Taib204a63BJxlHUfgl8PmfcRKdmWLiNt Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iEYEARECAAYFAlO1LsgACgkQ8dLMyEl6F222UgCgj6NGyelm+ZS36CUyHu7uJyuk CvwAn3956hvlmZWtnffimSre9qhqZXpk =rVyy -----END PGP SIGNATURE----- --Taib204a63BJxlHUfgl8PmfcRKdmWLiNt--