From owner-freebsd-fs@FreeBSD.ORG Fri Jul 5 10:30:47 2013 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by hub.freebsd.org (Postfix) with ESMTP id 80893E6F for ; Fri, 5 Jul 2013 10:30:47 +0000 (UTC) (envelope-from daniel@digsys.bg) Received: from smtp-sofia.digsys.bg (smtp-sofia.digsys.bg [193.68.21.123]) by mx1.freebsd.org (Postfix) with ESMTP id 045CC111B for ; Fri, 5 Jul 2013 10:30:46 +0000 (UTC) Received: from dcave.digsys.bg (dcave.digsys.bg [193.68.6.1]) (authenticated bits=0) by smtp-sofia.digsys.bg (8.14.6/8.14.6) with ESMTP id r65AUiOZ023679 (version=TLSv1/SSLv3 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO) for ; Fri, 5 Jul 2013 13:30:45 +0300 (EEST) (envelope-from daniel@digsys.bg) Message-ID: <51D6A054.2070704@digsys.bg> Date: Fri, 05 Jul 2013 13:30:44 +0300 From: Daniel Kalchev User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:17.0) Gecko/20130627 Thunderbird/17.0.7 MIME-Version: 1.0 To: freebsd-fs@freebsd.org Subject: Re: Slow resilvering with mirrored ZIL References: <2EF46A8C-6908-4160-BF99-EC610B3EA771@alumni.chalmers.se> <51D437E2.4060101@digsys.bg> <20130704000405.GA75529@icarus.home.lan> <20130704171637.GA94539@icarus.home.lan> <2A261BEA-4452-4F6A-8EFB-90A54D79CBB9@alumni.chalmers.se> <20130704191203.GA95642@icarus.home.lan> <43015E9015084CA6BAC6978F39D22E8B@multiplay.co.uk> <20130704202818.GB97119@icarus.home.lan> <8280798FCEE74CB08536F3BC43C9207F@multiplay.co.uk> In-Reply-To: <8280798FCEE74CB08536F3BC43C9207F@multiplay.co.uk> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 05 Jul 2013 10:30:47 -0000 On 05.07.13 02:21, Steven Hartland wrote: > > To give a concrete example which may well be of use for others, we > had a mysql box here with dual 60GB SSD L2ARC's whic after continuous > increases in query write traffic we ended up with total IO saturation. > > As a test we removed the L2ARC, partitioning them into a 10GB SLOG and > 40GB L2ARC and the machine was utterly transformed, from constant 100% > disk IO to 10% as the SLOG's soaked up the sync transfers from mysql. Also, you removed the ZFS fragmentation issue, which can severely impact performance. Unfortunately, this removes fragmentation for newly written data only, old data remains fragmented --- one can only dream for the day when the "block pointer rewrite" promise becomes reality... it could do wonders to ZFS. Alternatively, my proposal is for an background rewrite of ZFS blocks, that could at least achieve: re-distributing blocks to newly added vdevs, "fixing" compression/dedup of datasets, cleaning up fragmented data etc. It should be relatively easy to be implemented... (I am, unfortunately not offering coding help due to lack of time) Daniel