Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261512AbVE3EEj (ORCPT ); Mon, 30 May 2005 00:04:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261514AbVE3EEi (ORCPT ); Mon, 30 May 2005 00:04:38 -0400 Received: from rproxy.gmail.com ([64.233.170.206]:6501 "EHLO rproxy.gmail.com") by vger.kernel.org with ESMTP id S261512AbVE3EEf convert rfc822-to-8bit (ORCPT ); Mon, 30 May 2005 00:04:35 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:reply-to:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=ZEwAk7qa8g4kKARPuSJPOqP913f1IiIy8XIre+LS7Jke1UBrtLB4yBrESUgSPcqaE7iZ1ejO3lgowNWAc+VByrsbrZ6R8VvagoXiDv6TrDJWRAGut5P2eZqhdmMIa6VBXezTAk9Y4EysY4akDb9lcWHLbFSilzaehlJeNxiujpw= Message-ID: <311601c905052921046692cd3e@mail.gmail.com> Date: Sun, 29 May 2005 22:04:34 -0600 From: "Eric D. Mudama" Reply-To: "Eric D. Mudama" To: Greg Stark Subject: Re: [PATCH] SATA NCQ support Cc: Jens Axboe , Matthias Andree , linux-kernel@vger.kernel.org, jgarzik@pobox.com In-Reply-To: <87oeatxtw4.fsf@stark.xeocode.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Content-Disposition: inline References: <20050527070353.GL1435@suse.de> <20050527131842.GC19161@merlin.emma.line.org> <20050527135258.GW1435@suse.de> <429732CE.5010708@gmx.de> <20050527145821.GX1435@suse.de> <87oeatxtw4.fsf@stark.xeocode.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1408 Lines: 28 On 29 May 2005 23:41:31 -0400, Greg Stark wrote: > I would be interested to see those benchmarks people were posting earlier > claiming 30-40% difference retested with write caching disabled. I suspect > disabling write caching will demolish the non-NCQ performance but have a much > smaller effect on NCQ-enabled performance. > > Currently Postgres strongly recommends SCSI drives and the belief is that it's > the tagged command queuing that allows SCSI drives to perform well without > resorting to data integrity destroying write caching. If used properly, I don't feel write cache "destroys" data integrity, you just need to get your power failure tolerance elsewhere. ATA has a limitation of 32 tags, so queued write cache off won't beat unqueued write cache on in any modern drive. The real reason most SCSI drives do so well uncached is they use huge magnets with short, stiff actuators, smaller platters, and they spin significantly faster. NCQ certainly helps, but spending more money on mechanics makes a significant difference. Pick up a SCSI drive and an ATA drive, you'll feel the SCSI weighs seemingly twice as much. --eric - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/