Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751046AbWAYGgo (ORCPT ); Wed, 25 Jan 2006 01:36:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751048AbWAYGgo (ORCPT ); Wed, 25 Jan 2006 01:36:44 -0500 Received: from out4.smtp.messagingengine.com ([66.111.4.28]:35200 "EHLO out4.smtp.messagingengine.com") by vger.kernel.org with ESMTP id S1751043AbWAYGgn (ORCPT ); Wed, 25 Jan 2006 01:36:43 -0500 X-Sasl-enc: 5A2ZhEZdr+6FmUjlvkjz4O/pIDObpLx63S+3/Gk0RLAa 1138171001 Message-ID: <43D71C75.2050807@fastmail.co.uk> Date: Wed, 25 Jan 2006 14:36:37 +0800 From: Max Waterman User-Agent: Thunderbird 1.6a1 (Macintosh/20060122) MIME-Version: 1.0 To: Ian Soboroff CC: linux-kernel@vger.kernel.org Subject: Re: io performance... References: <43CB4CC3.4030904@fastmail.co.uk> <43CD2405.4070902@cfl.rr.com> <43CDED23.5060701@fastmail.co.uk> <43CE5C7A.5060608@cfl.rr.com> <43D07C08.5000903@fastmail.co.uk> <9cfek33vwvo.fsf@nist.gov> In-Reply-To: <9cfek33vwvo.fsf@nist.gov> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3131 Lines: 47 Ian Soboroff wrote: > Max Waterman writes: > >> Phillip Susi wrote: >>> Right, the kernel does not know how many disks are in the array, so >>> it can't automatically increase the readahead. I'd say increasing >>> the readahead manually should solve your throughput issues. >> Any guesses for a good number? >> >> We're in RAID10 (2+2) at the moment on 2.6.8-smp. These are the block >> numbers I'm getting using bonnie++ : >> >> [...] >> We're still wondering why rd performance is so low - seems to be the >> same as a single drive. RAID10 should be the same performance as RAID0 >> over two drives, shouldn't it? > > I think bonnie++ measures accesses to many small files (INN-like > simulation) and database accesses. These are random accesses, which > is the worst access pattern for RAID. Seek time in a RAID equals the > longest of all the drives in the RAID, rather than the average. So > bonnie++ is domninated by your seek time. You think so? I had assumed when bonnie++'s output said 'sequential access' that it was the opposite of random, for example (raid0 on 5 drives) : > +---------------------------------------------------------------------------------------------------------------------------------------------------+ > | |Sequential Output |Sequential Input | | |Sequential Create |Random Create | > |---------------------+------------------------------+--------------------|Random |-----+----------------------------+----------------------------| > | |Size:Chunk|Per Char |Block |Rewrite |Per Char |Block |Seeks |Num |Create |Read |Delete |Create |Read |Delete | > | |Size | | | | | | |Files| | | | | | | > |---------------------+---------+----------+---------+---------+----------+---------+-----+--------+---------+---------+--------+---------+---------| > | |K/sec|% |K/sec |% |K/sec|% |K/sec|% |K/sec |% |/ sec|% | |/ |% |/ sec|% |/ sec|% |/ |% |/ sec|% |/ sec|% | > | | |CPU| |CPU| |CPU| |CPU| |CPU| |CPU| |sec |CPU| |CPU| |CPU|sec |CPU| |CPU| |CPU| > |---------------------+-----+---+------+---+-----+---+-----+---+------+---+-----+---+-----+----+---+-----+---+-----+---+----+---+-----+---+-----+---| > |hostname |2G |48024|96 |121412|13 |59714|10 |47844|95 |200264|21 |942.8|1 |16 |4146|99 |+++++|+++|+++++|+++|4167|99 |+++++|+++|14292|99 | > +---------------------------------------------------------------------------------------------------------------------------------------------------+ Am I wrong? If so, what exactly does 'Sequential' mean in this context? Max. - 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/