From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda3.sgi.com [192.48.176.15]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id q6I2IJMq134737 for ; Tue, 17 Jul 2012 21:18:19 -0500 Received: from greer.hardwarefreak.com (mo-65-41-216-221.sta.embarqhsd.net [65.41.216.221]) by cuda.sgi.com with ESMTP id 0hRUZ19I4NwbiJwL for ; Tue, 17 Jul 2012 19:18:18 -0700 (PDT) Received: from [192.168.100.53] (gffx.hardwarefreak.com [192.168.100.53]) by greer.hardwarefreak.com (Postfix) with ESMTP id B75AD6C1AF for ; Tue, 17 Jul 2012 21:18:17 -0500 (CDT) Message-ID: <50061CEA.4070609@hardwarefreak.com> Date: Tue, 17 Jul 2012 21:18:18 -0500 From: Stan Hoeppner MIME-Version: 1.0 Subject: Re: A little RAID experiment References: <5004875D.1020305@hardwarefreak.com> <5004C243.6040404@hardwarefreak.com> <20120717052621.GB23387@dastard> In-Reply-To: <20120717052621.GB23387@dastard> Reply-To: stan@hardwarefreak.com List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: xfs@oss.sgi.com On 7/17/2012 12:26 AM, Dave Chinner wrote: ... > I bet it's single threaded, which means it is: The data given seems to strongly suggest a single thread. > Which means throughput is limited by IO latency, not bandwidth. > If it takes 10us to do the write(2), issue and process the IO > completion, and it takes 10us for the hardware to do the IO, you're > limited to 50,000 IOPS, or 200MB/s. Given that the best being seen > is around 35MB/s, you're looking at around 10,000 IOPS of 100us > round trip time. At 5MB/s, it's 1200 IOPS or around 800us round > trip. > > That's why you get different performance from the different raid > controllers - some process cache hits a lot faster than others. ... > IOWs, welcome to Understanding RAID Controller Caching Behaviours > 101 :) It would be somewhat interesting to see Stefan's latency and throughput numbers for 4/8/16 threads. Maybe the sysbench "--num-threads=" option is the ticket. The docs state this is for testing scheduler performance, and it's not clear whether this actually does threaded IO. If not, time for a new IO benchmark. -- Stan _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs