From owner-freebsd-stable@FreeBSD.ORG Sun Jan 4 01:49:17 2009 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 93CCF106566B for ; Sun, 4 Jan 2009 01:49:17 +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 54F028FC13 for ; Sun, 4 Jan 2009 01:49:16 +0000 (UTC) (envelope-from andrew@modulus.org) Received: by email.octopus.com.au (Postfix, from userid 1002) id 4508D173C9; Sun, 4 Jan 2009 12:33:09 +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] (ppp121-44-54-147.lns10.syd7.internode.on.net [121.44.54.147]) (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 41FF917265; Sun, 4 Jan 2009 12:33:05 +1100 (EST) Message-ID: <496011CC.2010201@modulus.org> Date: Sun, 04 Jan 2009 12:33:00 +1100 From: Andrew Snow User-Agent: Thunderbird 2.0.0.14 (X11/20080523) MIME-Version: 1.0 To: Pete French References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-stable@freebsd.org Subject: Re: slow zvol performance compared to files on the same pool X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 04 Jan 2009 01:49:17 -0000 Pete French wrote: > I was experimenting with iscsi earlier, using both a flat file as the > backing store and also a zvol. I noticed that the zvol was giving me > dreadful performance - reading at about 20 meg/second and writing at > about 12. the fklat file gives about 45 meg/second both ways. > > i thouht it was to do wuth the iscsi layer, but I then tried it using > dd on the machinbe itself and got the same results. it seems very > curious - I am creating both the filesystem for the iscsi file and the > zvol on the same pool, so the underlying discs (4 x 15k SCSI drives on > U320) are the same in both places, as is the pool. > > anybody got any opinions ? this is on 7.1-RC2, but I have nothing else > to compare it to. On 7.x (where ZFS is really quite broken for server use - don't waste too much time on it) the ZVOL code did an "fsync" after every single block write. Its a testament to your fast disks that you got as high as 12mb/s. I don't know why your read speed was so bad, but you should try again on 8-current as numerous fixes and improvements have happened. - Andrew