From mboxrd@z Thu Jan 1 00:00:00 1970 From: Brad Campbell Subject: Re: RAID5 alignment issues with 4K/AF drives (WD green ones) Date: Fri, 30 Dec 2011 14:24:40 +0800 Message-ID: <4EFD5928.100@fnarfbargle.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Michele Codutti Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 30/12/11 07:28, Michele Codutti wrote: > Hi all, I'm writing to this mailing list because I cannot figure out why I had some performance issues with my three WD20EARS (2TB Western Digital "Green" 4K/AF drive). > These drives has a (sequential) write throughput around 100MB/s. When I combine them in a RAID0 configuration the throughput is around 300 MB/s and in a RAID1 configuration they preserve a single drive performance of 100MB/s. > When I combine all three drives in a RAID5 configuration the (individual) performance falls around 40MB/s. > I get the same performance level when I do individual misaligned writes (ex: dd if=/dev/zero bs=6K of=/dev/sda). > The drives are not partitioned. I'm using the default chunk size (512K) and the default metadata superblock version (1.2). > I had not formatted the RAID or any single drive during my test i had directly used the raw devices. > I'm using a 11.10 ubuntu with 3.0.0 linux kernel and 3.1.4 mdadm. > The hardware is a HP microserver. > Just a thought, but do you have the "XP mode" jumper removed on all drives? Regards, Brad