From mboxrd@z Thu Jan 1 00:00:00 1970 From: Loic Dachary Subject: Re: durability model Date: Tue, 27 May 2014 16:24:16 +0200 Message-ID: <5384A010.4080300@dachary.org> References: <1401131148.7008.YahooMailNeo@web165003.mail.bf1.yahoo.com> <1401197435.39621.YahooMailNeo@web165002.mail.bf1.yahoo.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="snRcx02WKc7mSS1PCf940Ol6RpGuEK3AQ" Return-path: Received: from smtp.dmail.dachary.org ([91.121.254.229]:50173 "EHLO smtp.dmail.dachary.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751913AbaE0OYp (ORCPT ); Tue, 27 May 2014 10:24:45 -0400 In-Reply-To: <1401197435.39621.YahooMailNeo@web165002.mail.bf1.yahoo.com> Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Koleos Fuskus Cc: Kyle Bader , Ceph Development This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --snRcx02WKc7mSS1PCf940Ol6RpGuEK3AQ Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 27/05/2014 15:30, Koleos Fuskus wrote:> Hi Kyle, > Thanks for your answer! > I have other questions regarding the model. Sorry, I accumulated differ= ent doubts and the e-mail is a bit long. >=20 > 1. What will be erasure model unit? Is it a pool or a placement group? = I cannot see the best option here yet, probably because my inexperience w= ith Ceph. A pool.=20 > 2. Crush_ruleset for erasured pools: Are these crush-ruleset impacting = on the reliability model? Should I define a default crush-ruleset?=20 Unless I'm mistaken, the crush ruleset is only relevant to the durability= model to the extent that it defines the failure domain. If a ruleset req= uires that no two shards of a given placement group (i.e. no two shards o= f a given object since a placement group is a set of object that share th= e same OSD for a given shard) are on the same host, it will lead to a mod= el that is different from a ruleset that requires that no two shards are = in the same datacenter. > 3. Metadata: Jerasure creates metadata files. How are those files store= d in ceph (what kind of redundancy)? Should I care about them? I guess th= e jerasure metafiles are not important. If all objects stored in a pool s= hare the same erasure-code-k and erasure-code-m, then is easy to re-gener= ate the metadata file. However, if metadata file is lost and the pool con= tains erasured objects with different k and m, then repairing data will n= ot be possible. Should I ignore this problem? Could you confirm that each= pool has the same erasure parameters? Jerasure does not create a metadata file. > 4. Number of PG for an erasured-pool. The total PGs in the case of repl= ication is calculated with this formula: Total PGs=3D (OSDs * 100)/Replic= as. > > Should I replace Replicas for the stretch factor (storage overhead) in = the case of erasure? >=20 > 5.Parameters - Default values: > erasure-code-k (default 4) > erasure-code-m (default 2) >=20 > OSD (default 200) > PG (default 100 x OSD) > stripes (default ????) I proposed an update to the documentation to clarify this : https://githu= b.com/ceph/ceph/pull/1856 . Does it look sensible to you ? Cheers > 6. Units > It is hardcoded on the reliable tool: > KiB =3D 1000 > MiB =3D KiB * 1000 > GiB =3D MiB * 1000 > TiB =3D GiB * 1000 > PiB =3D TiB * 1000 >=20 > Why KiB is 1000 when should be 1024? > Best,=20 > Koleosfuscus >=20 --=20 Lo=EFc Dachary, Artisan Logiciel Libre --snRcx02WKc7mSS1PCf940Ol6RpGuEK3AQ 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/ iEYEARECAAYFAlOEoBcACgkQ8dLMyEl6F22T1gCfcdsYWoMjOYb5JmYS3YMnCzom u58AnRwM5G5VFXJg/Kzl2E9+mocFZhOh =69od -----END PGP SIGNATURE----- --snRcx02WKc7mSS1PCf940Ol6RpGuEK3AQ--