From owner-freebsd-fs@FreeBSD.ORG Thu Jan 24 08:33:01 2013 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.FreeBSD.org [8.8.178.115]) by hub.freebsd.org (Postfix) with ESMTP id 6FF4A224 for ; Thu, 24 Jan 2013 08:33:01 +0000 (UTC) (envelope-from borjam@sarenet.es) Received: from proxypop04.sare.net (proxypop04.sare.net [194.30.0.65]) by mx1.freebsd.org (Postfix) with ESMTP id 34AFFEAA for ; Thu, 24 Jan 2013 08:33:00 +0000 (UTC) Received: from [172.16.2.2] (izaro.sarenet.es [192.148.167.11]) by proxypop04.sare.net (Postfix) with ESMTPSA id A75C69DD7DF; Thu, 24 Jan 2013 09:32:47 +0100 (CET) Subject: Re: RFC: Suggesting ZFS "best practices" in FreeBSD Mime-Version: 1.0 (Apple Message framework v1085) Content-Type: text/plain; charset=us-ascii From: Borja Marcos In-Reply-To: <81460DE8-89B4-41E8-9D93-81B8CC27AA87@baaz.fr> Date: Thu, 24 Jan 2013 09:32:58 +0100 Content-Transfer-Encoding: quoted-printable Message-Id: <8BA7B786-3B4B-473B-B4F0-798C9B5AEF00@sarenet.es> References: <314B600D-E8E6-4300-B60F-33D5FA5A39CF@sarenet.es> <565CB55B-9A75-47F4-A88B-18FA8556E6A2@samsco.org> <81460DE8-89B4-41E8-9D93-81B8CC27AA87@baaz.fr> To: Jean-Yves Moulin X-Mailer: Apple Mail (2.1085) Cc: FreeBSD Filesystems , Scott Long 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: Thu, 24 Jan 2013 08:33:01 -0000 On Jan 23, 2013, at 4:16 PM, Jean-Yves Moulin wrote: > But what about battery-backed cache RAID card ? They offer a = non-volatile cache that improves writes. And this cache is safe because = of the battery. These feature doesn't exist on bare disks. They can be "fine" for certain applications, especially with limited = ability filesystems. But we are speaking about using maybe the latest = and greatest in filesystem technology, with a superior mechanism to manage redundancy = and I/O bandwidth. Using another redundancy mechanism underneath can make matters worse, with one system working against the other. ZFS manages it better. ZFS allows you to decide if you need to cache = metadata and/or data or none of them. RAID cards can show stupid caching = behaviors depending on your workload. So, RAID card with ZFS, definitely a no-no. As Scott said, more failure = modes. And some of them, complex. Many trivial operations may require a = reboot. The card hides important disk diagnostics from ZFS. Borja.