From owner-freebsd-fs@FreeBSD.ORG Mon Oct 6 00:02:09 2008 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 70E4E1065688 for ; Mon, 6 Oct 2008 00:02:09 +0000 (UTC) (envelope-from andrew@modulus.org) Received: from email.octopus.com.au (host-122-100-2-232.octopus.com.au [122.100.2.232]) by mx1.freebsd.org (Postfix) with ESMTP id 30F308FC18 for ; Mon, 6 Oct 2008 00:02:08 +0000 (UTC) (envelope-from andrew@modulus.org) Received: by email.octopus.com.au (Postfix, from userid 1002) id 31E8D17DB1; Mon, 6 Oct 2008 10:02:07 +1000 (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=-0.1 required=10.0 tests=ALL_TRUSTED,DNS_FROM_DOB, DNS_FROM_SECURITYSAGE,RCVD_IN_DOB autolearn=no version=3.2.3 Received: from [10.20.30.100] (60.218.233.220.exetel.com.au [220.233.218.60]) (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 D121D17306; Mon, 6 Oct 2008 10:02:02 +1000 (EST) Message-ID: <48E9556C.9060004@modulus.org> Date: Mon, 06 Oct 2008 11:01:48 +1100 From: Andrew Snow User-Agent: Thunderbird 1.5.0.9 (Windows/20061207) MIME-Version: 1.0 To: Dimitar Vasilev References: <59adc1a0810051210t4a3503aci2bc06ba0aa5376c3@mail.gmail.com> In-Reply-To: <59adc1a0810051210t4a3503aci2bc06ba0aa5376c3@mail.gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-fs@freebsd.org Subject: Re: zfs as layer distributor 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: Mon, 06 Oct 2008 00:02:09 -0000 Dimitar Vasilev wrote: > Hi all, > Does someone use zfs as layer distributor on the top of hardware raid - > (RAID10,RAID6,etc)? I've found ZFS works faster when given more than one disk device. The reason being, it is smart about writing journal logs and metadata copies to different devices, resulting in higher performance by using idle disks. It also provides more "channels" for write clustering so higher throughput on write-heavy loads. Secondly if you use ZFS to provide RAID1 or RAID5, due to checksumming it can be smarter about which data it chooses in the event of a checksum failure. Hardware RAID can only do this with RAID6. Finally, when ZFS issues "flush cache" command to the disk for metadata and journal logs, there is less data to flush when you give it multiple smaller devices. If you have a single monolithic RAID device with a large (eg. 256mb) cache, it can ruin performance while the RAID card flushes its entire cache. (This can be disabled with a sysctl). - Andrew