From mboxrd@z Thu Jan 1 00:00:00 1970 From: Loic Dachary Subject: Re: Mojette based Erasure Code is more performant than ISA-L or Jerasure (or not) Date: Wed, 20 Apr 2016 23:31:23 +0700 Message-ID: <5717AEDB.8050707@dachary.org> References: <57177CF7.1090600@dachary.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from smtp26.services.sfr.fr ([93.17.128.1]:36213 "EHLO smtp26.services.sfr.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751126AbcDTQbj (ORCPT ); Wed, 20 Apr 2016 12:31:39 -0400 In-Reply-To: Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Chandan Kumar Singh Cc: ceph-devel@vger.kernel.org On 20/04/2016 20:10, Chandan Kumar Singh wrote: > Hi >=20 > Here is the link for the benchmark study : > http://arxiv.org/pdf/1504.07038.pdf. Initially, the mailing list was > blocking it because of HTML subparts. I meant that the first step would be to repeat the benchmark as describ= ed in the paper. Unless I missed something the details of how the resul= ts were obtained have not been published. It is enough to get just one = detail wrong and see significantly different results.=20 Here is an example. From an implementor point of view, the performance = difference that matters is when reading data that has not been damaged = (i.e. what happens 99.99% of the time). Mojette does not have systemati= c code. What it means is that reading data always requires decoding chu= nks. With systematic code, which is what jerasure / isa-l offer and wha= t Ceph uses, reading erasure coded data does not require decoding. This= is the Achilles' heel of this erasure code method. It is supposed to b= e measured by the graph in figure 3. For instance the bottom of figure = 3 states that ISA-L requires 640 cycles to read 8KB while Mojette requi= res 1750 when there is no erasure (i.e. no chunk lost). That makes litt= le sense to me as you don't need ISA-L at all to read the original 8KB = (that's what systematic codes are good for). This detail would need to = be clarified before the experiment can be repeated. Mojette is definitely interesting and it would be nice to see Free Soft= ware minded people working on it. There is a long way to go before it's= useable, but exploring new avenues is fascinating :-) Cheers =20 > Regards > Chandan >=20 > On Wed, Apr 20, 2016 at 6:28 PM, Loic Dachary wrot= e: >> Hi, >> >> On 20/04/2016 15:52, Chandan Kumar Singh wrote: >>> Hi >>> >>> The authors of Mojette Erasure Encoding claim that this EC has hig= her >>> performance than ISA-L and Jerasure and can be used for hot storage >>> use cases. Their EC is used in open source RozoFS. What is your >>> evaluation of it? It will be nice if it is available as another EC >>> plugin. >> >> RozoFS is no longer developped (last commit was july last year). It = would be nice to have an alternative implementation of the same algorit= hm, well maintained. It's sad to see Free Software being frozen. But Fr= ee Software is never dead, all it needs is good will and a little work = to be resurected ! I've never seen any benchmark regarding performances= , that would be the first step. >> >> Cheers >> >> -- >> Lo=C3=AFc Dachary, Artisan Logiciel Libre >> >=20 --=20 Lo=C3=AFc Dachary, Artisan Logiciel Libre -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html