From owner-freebsd-fs@FreeBSD.ORG Sat Jan 10 02:38:55 2009 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 91CD5106566C for ; Sat, 10 Jan 2009 02:38:55 +0000 (UTC) (envelope-from andrew@modulus.org) Received: from email.octopus.com.au (email.octopus.com.au [122.100.2.232]) by mx1.freebsd.org (Postfix) with ESMTP id 4CAEC8FC08 for ; Sat, 10 Jan 2009 02:38:55 +0000 (UTC) (envelope-from andrew@modulus.org) Received: by email.octopus.com.au (Postfix, from userid 1002) id 3B8EF17E3F; Sat, 10 Jan 2009 13:38:54 +1100 (EST) X-Spam-Checker-Version: SpamAssassin 3.2.3 (2007-08-08) on email.octopus.com.au X-Spam-Level: X-Spam-Status: No, score=-1.4 required=10.0 tests=ALL_TRUSTED autolearn=failed version=3.2.3 Received: from [10.1.50.60] (ppp121-44-0-132.lns10.syd7.internode.on.net [121.44.0.132]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: admin@email.octopus.com.au) by email.octopus.com.au (Postfix) with ESMTP id A0C8617D9C; Sat, 10 Jan 2009 13:38:48 +1100 (EST) Message-ID: <49680A26.1020502@modulus.org> Date: Sat, 10 Jan 2009 13:38:30 +1100 From: Andrew Snow User-Agent: Thunderbird 2.0.0.14 (X11/20080523) MIME-Version: 1.0 To: fbsd@dannysplace.net, freebsd-fs@freebsd.org References: <20081031033208.GA21220@icarus.home.lan> <491C5AA7.1030004@samsco.org> <491C9535.3030504@dannysplace.net> <4920E1DD.7000101@dannysplace.net> <20081117070818.GA22231@icarus.home.lan> <496549D9.7010003@dannysplace.net> <4966B6B1.8020502@dannysplace.net> <496712A2.4020800@dannysplace.net> In-Reply-To: <496712A2.4020800@dannysplace.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Subject: Re: Areca vs. ZFS performance testing. 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: Sat, 10 Jan 2009 02:38:55 -0000 ZFS does not require battery-backed disk cache, as long as disks and controller flush their cache when they are told to by the OS. Then ZFS only issues sync/flush commands for the ZIL (transaction log), but majority of I/Os are free to sit in cache to complete when they are ready. Data that is not fsync()'d by the application may be lost on power outage, but stuff like databases do fsync() so they are protected. - Andrew