From mboxrd@z Thu Jan 1 00:00:00 1970 From: Loic Dachary Subject: Re: Reliability model for RADOS - effects during second failures Date: Thu, 03 Jul 2014 09:10:37 +0200 Message-ID: <53B501ED.7070005@dachary.org> References: Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="nPuBuRs4NbpHCA1UE59T9g6fIuA0u2tJD" Return-path: Received: from mail2.dachary.org ([91.121.57.175]:36552 "EHLO smtp.dmail.dachary.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751250AbaGCHKq (ORCPT ); Thu, 3 Jul 2014 03:10:46 -0400 In-Reply-To: Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Koleos Fuscus Cc: "ceph-devel@vger.kernel.org" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --nPuBuRs4NbpHCA1UE59T9g6fIuA0u2tJD Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Hi koleosfuscus, On 03/07/2014 00:33, Koleos Fuscus wrote: > Hi Kyle, Loic, >=20 > The current code uses a =E2=80=9CFIT rate multiplier=E2=80=9D to includ= e for instance > the effect of operations done in parallel. That multiplier (n) has an > effect on Pfail. In the initial failure, it is calculated using the > number of replicas and the stripe count as seen in > https://github.com/ceph/ceph-tools/blob/master/models/reliability/Rados= Rely.py#L86. >=20 > The thing that doesn=E2=80=99t have sense to me is the way the multipli= er is > calculated for the failure of the remaining copies in > https://github.com/ceph/ceph-tools/blob/master/models/reliability/Rados= Rely.py#L92 > Why the stripes are not taking into account? What is the purpose of > using the =E2=80=9Cdeclustering factor=E2=80=9D on that equation? Is th= at equation > correct? I read this note by sage > https://www.mail-archive.com/ceph-devel@vger.kernel.org/msg01650.html > trying to clarify the role of PGs but didn=E2=80=99t help me to underst= and it. At the risk of adding confusion to the discussion, does the current relia= bility model make room to take into account what is described in anrg.usc= =2Eedu/~maheswaran/Xorbas.pdf under "4. Reliability Analysis" ? In other = words, is there a place where one could set things like "disk fail % of t= he time" and "network is X Gb/s" and "repairing a disk failure requires d= isk 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 Marko= v model is useful. > Besides, I have a simple question related with the equation on L86 for > the initial failure. The stripping process splits user content in > #number of objects, which equivalent to the stripe count. That group > of objects constitutes an object set. Each object is composed by one > or more stripes units. All stripes units (stripe count) are written in > parallel. Typically each object is mapped to a different disk. What > happen when the object set is full and a new object is started? Are > this new objects assigned to same disks used for the previous full > object set? In an ideal situation, if a disk / OSD is full it means the whole cluster= is full. Is it reasonable to ignore this situation when thinking about t= he reliability model ? If not could you explain how ? Cheers=20 >=20 > Best >=20 > koleosfuscus >=20 > ________________________________________________________________ > "My reply is: the software has no known bugs, therefore it has not > been updated." > Wietse Venema >=20 --=20 Lo=C3=AFc Dachary, Artisan Logiciel Libre --nPuBuRs4NbpHCA1UE59T9g6fIuA0u2tJD 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/ iEYEARECAAYFAlO1Ae0ACgkQ8dLMyEl6F20HbwCgoQTB2+TSa8WpXafoEXxNCG2L IisAnRP7+SktxWGHQx4hjJvmhqZOBjze =iJbZ -----END PGP SIGNATURE----- --nPuBuRs4NbpHCA1UE59T9g6fIuA0u2tJD--