From owner-freebsd-fs@FreeBSD.ORG Thu May 12 08:45:05 2011 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 8353C1065687 for ; Thu, 12 May 2011 08:45:05 +0000 (UTC) (envelope-from numisemis@gmail.com) Received: from mail-ww0-f50.google.com (mail-ww0-f50.google.com [74.125.82.50]) by mx1.freebsd.org (Postfix) with ESMTP id 061F38FC20 for ; Thu, 12 May 2011 08:45:04 +0000 (UTC) Received: by wwc33 with SMTP id 33so1449722wwc.31 for ; Thu, 12 May 2011 01:45:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:subject:mime-version:content-type:from :in-reply-to:date:cc:message-id:references:to:x-mailer; bh=plLgz8RQpu1MLLWCuOQcV4ARzhPOFTu9RwDrXTs5wgw=; b=FrakORjqE3gRQfauCysMMMTNxZHu4vR9CTnKbXQfPiJtBogU8YAfkuN/+yCa3x60Sk jRdNsKlkMg2JW+Ic5cx97ZnUrKFsXBduYhxYd56iCt+WymLPpj/9jkfk3X0pQo/9SxWp mg/GZNpMt0lj/Av2WZewBbfLzaF/EMgxby428= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=subject:mime-version:content-type:from:in-reply-to:date:cc :message-id:references:to:x-mailer; b=AUmwpc5ZjQz/Enf680Jl7SiWUBrLkU5W9K2rYvOSOxCdrVr2kVf8OxLozXOJ56Rq2v BbhNofEA/ziFWboG5wHhtBqVPojor7JwMQKzeFfXbdzB7zMdo+nWMFaLDYp4J3rZnlxW LENcru6LLwRjrSeoSxTRw6zL5jmuuIRJymu7s= Received: by 10.216.69.140 with SMTP id n12mr7610262wed.32.1305189903478; Thu, 12 May 2011 01:45:03 -0700 (PDT) Received: from sime-imac.logos.hr ([213.147.110.159]) by mx.google.com with ESMTPS id f52sm487017wes.35.2011.05.12.01.45.02 (version=TLSv1/SSLv3 cipher=OTHER); Thu, 12 May 2011 01:45:03 -0700 (PDT) Mime-Version: 1.0 (Apple Message framework v1084) From: =?iso-8859-2?Q?=A9imun_Mikecin?= In-Reply-To: <20110512083429.GA58841@icarus.home.lan> Date: Thu, 12 May 2011 10:45:01 +0200 Message-Id: References: <4DCA5620.1030203@dannysplace.net> <4DCB455C.4020805@dannysplace.net> <20110512033626.GA52047@icarus.home.lan> <4DCB7F22.4060008@digsys.bg> <20110512083429.GA58841@icarus.home.lan> To: Jeremy Chadwick X-Mailer: Apple Mail (2.1084) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Cc: freebsd-fs Subject: Re: ZFS: How to enable cache and logs. X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 12 May 2011 08:45:05 -0000 On 12. svi. 2011., at 10:34, Jeremy Chadwick wrote: >=20 > I had no idea the primary point of a SLOG was to deal with = applications > that make use of O_SYNC. I thought it was supposed to improve write > performance for both asynchronous and synchronous writes. Obviously = I'm > wrong here. If the application is not using O_SYNC, write operation returns to the = app before the data is actually written. > What guarantee is there that the intent log -- which is written to the > disk -- actually got written to the disk in the middle of a power > failure? There's a lot of focus there on the idea that "the intent = log > will fix everything, but may lose writes", but what guarantee do I = have > that the intent log isn't corrupt or botched during a power failure? I expect that checksumming also works for ZIL (anybody knows?). If that = is the case, corruption would be detected, but you will have lost data = unless you are using mirrored slog devices.