From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755960AbYE0Aem (ORCPT ); Mon, 26 May 2008 20:34:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753328AbYE0Aeb (ORCPT ); Mon, 26 May 2008 20:34:31 -0400 Received: from smtp-out.google.com ([216.239.33.17]:30995 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752093AbYE0Aea (ORCPT ); Mon, 26 May 2008 20:34:30 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=received:message-id:date:from:to:subject:cc:in-reply-to: mime-version:content-type:content-transfer-encoding: content-disposition:references; b=RtD2nVPrqWqZhBFLQOrD3NbiH9JhnOaQmBPyHfbuokWZF3HFW8rD+2AcSmoT/y9It wCG05HSo77O+XibedUVwg== Message-ID: Date: Mon, 26 May 2008 17:34:25 -0700 From: "Grant Grundler" To: "Mark Lord" Subject: Re: Marvell 88SX7042 [4 Port SATA PCI-Express x4] Support/Questions Cc: "Justin Piszcz" , "Jeff Garzik" , linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org In-Reply-To: <4839A63E.4050409@rtr.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <4839A63E.4050409@rtr.ca> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, May 25, 2008 at 10:47 AM, Mark Lord wrote: ... > Sure, if the bus and memory are fast enough. You'll hit the Linux/libata > transactions/sec limit at some point, but I don't know what that is. > > Eg. Here's a 4X (I think) card in my PCIe video slot: > > beefy:~# mdadm --create /dev/md0 --chunk=256 -l 0 --raid-devices=4 > /dev/sd[bcde] > mdadm: array /dev/md0 started. > > beefy:~# hdparm -t --direct /dev/sd[bcde] /dev/md0 > > /dev/sdb: > Timing O_DIRECT disk reads: 218 MB in 3.01 seconds = 72.46 MB/sec > > /dev/sdc: > Timing O_DIRECT disk reads: 256 MB in 3.01 seconds = 85.00 MB/sec > > /dev/sdd: > Timing O_DIRECT disk reads: 192 MB in 3.01 seconds = 63.79 MB/sec > > /dev/sde: > Timing O_DIRECT disk reads: 256 MB in 3.01 seconds = 85.07 MB/sec > > /dev/md0: > Timing O_DIRECT disk reads: 768 MB in 3.00 seconds = 255.69 MB/sec The bottle neck here is with the four disks. Modern 1TB 7200 rpm disks have raw throughput rates up to around 100MB/s. Anything in the last 4-5 years should do better than 60MB/s. In theory, ~16 disks (4 disks per 7042 port using Port Mulitpliers), one should be able to hit 200+ MB/s per 7042 port and approach 900MB/s total. Getting more than 900Mb/s will depend on the chipset. IIRC, the MMRBC of 128 bytes will result in about 15% protocol overhead in the PCI-e link. Bigger PCI-e "burst" will result in dramatically less overhead (IIRC, 256Byte == 9% overhead.) hth, grant