From owner-freebsd-fs@FreeBSD.ORG Fri Jan 1 20:33:47 2010 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 32D9D1065672 for ; Fri, 1 Jan 2010 20:33:47 +0000 (UTC) (envelope-from numisemis@yahoo.com) Received: from web112405.mail.gq1.yahoo.com (web112405.mail.gq1.yahoo.com [98.137.26.137]) by mx1.freebsd.org (Postfix) with SMTP id 012E78FC14 for ; Fri, 1 Jan 2010 20:33:46 +0000 (UTC) Received: (qmail 88803 invoked by uid 60001); 1 Jan 2010 20:06:57 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.com; s=s1024; t=1262376417; bh=2N6gM5ZEM9rb418nV2kIyFQrZMZnYh9oeD/akhYq/NQ=; h=Message-ID:X-YMail-OSG:Received:X-Mailer:Date:From:Subject:To:Cc:MIME-Version:Content-Type:Content-Transfer-Encoding; b=fANy8f9ddKKFd3hsBbO5sOsex+9Wi3K6ru90VcC+WNbuvrjCJfJbWUmYIS03J0fKMXKqaAfO5QV2uN99UHOt/oime3Qn6487S7tAN/SbMEWgpDYDgeC6vEEu+HBshvj3uUrVPFv54BwpY8t1qIwB7uENEPAO20dSiVi1X/yR6SM= DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:X-YMail-OSG:Received:X-Mailer:Date:From:Subject:To:Cc:MIME-Version:Content-Type:Content-Transfer-Encoding; b=Wv7St4Vga00po3vsWKQvXvVUQoWxEFKi+/mzmQiFr7d9cfcevHbZuDbzTLgorb0n9VujuqGqT8bMGGSYsdLE1WPnfPcRW8tE/x2Vi1H8GXHWoKjkHAn29XKk80jTgt6MrKaS1OxGCZTNBtyNc080P76cWs0Fp8sPbd55rOIkRW4=; Message-ID: <55389.88569.qm@web112405.mail.gq1.yahoo.com> X-YMail-OSG: 93BjT.gVM1leEIxe88uXv4Z2Gh_sJNZCytYWlD_LEbayd5Qx6klRM.e6S6mVtg7gEi3whZO6lrG.YrURnkRtFvJHPgEriCfamPdHOAYnwCUL_tWPMthFBDuMV6DtfTIWxrFRLthCTIq_VrvH5J_iOF4L6r7TBWks.yRrygu8oeHHFxMxKxTnBg3Qp3HLCKrUrHuxFlieyjF5F1SWGq7Ko7m6lKeTWanK8JTCq5x2HugAqc73LCRP_eRjnF.hGYgKYP38a146.84z_LVU2hQ1dHyUbVybCzVVfEMH7wqGwTkUz_nBB0SeO8QYyRTTvZkwHMq.sDvirHBVZ4QsqqElLU2aGEtsFwFPlfeoL_uf0g8FIqU6KKb2Oa_r_RWpKq7VAr._.iDni5LbM1S2wpflNdNfdA7stuWBGMmyXYA- Received: from [87.248.121.166] by web112405.mail.gq1.yahoo.com via HTTP; Fri, 01 Jan 2010 12:06:56 PST X-Mailer: YahooMailWebService/0.8.100.260964 Date: Fri, 1 Jan 2010 12:06:56 -0800 (PST) From: =?utf-8?B?xaBpbXVuIE1pa2VjaW4=?= To: "ticso@cicely.de" MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Cc: "freebsd-fs@freebsd.org" , Danny Carroll Subject: Re: ZFS RaidZ2 with 24 drives? 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: Fri, 01 Jan 2010 20:33:47 -0000 =0A1. sij. 2010., u 20:51, Bernd Walter napisao:= =0A=0AOn Fri, Jan 01, 2010 at 10:56:21AM -0600, Bob Friesenhahn wrote:=0AOn= Fri, 1 Jan 2010, Danny Carroll wrote:=0A=0AYou do not have this protection= when ZFS has access to the raw devices.=0AEven worse if the devices write = cache is turned on.=0A=0AThis statement does not appear to be true. ZFS wi= ll always request =0Athat devices flush their cache. The only time there i= s no =0A"protection" is if the device ignores that flush request and the ca= che =0Ais volatile. Controller battery-backed RAM is useful since the =0Ac= ontroller can respond to the cache flush request once the data is in =0Abat= tery-backed RAM, thereby dramatically improving write latencies for =0Asmal= l writes=0A=0AWhich - if it is true for the controller - can be dangerous.= =0AA battery backed cache is volatile if the system is going down for=0Aa l= ong time.=0AOr consider the system is going down to relocate the disks to a= new=0Amachine, or just to a newer controller?=0A=0A=0AIf you are using amr= driver then FreeBSD will flush cache during shutdown. Haven't tried other = drivers myself, but I suppose they also do the same.=0AYou can have a probl= em only on unclean shutdown after which you didn't reboot (nobody does that= willingly).=0A=0A=0A