From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oliver Martin Subject: Re: LVM performance Date: Fri, 22 Feb 2008 14:41:45 +0100 Message-ID: <47BED119.4070000@student.tuwien.ac.at> References: <18360.8065.335494.142060@tree.ty.sabi.co.UK> <20080217074526.29d3c5c5@hardcode42.net> <20080218062604.05ae4821@szpak> <20080218154203.6e2d1483@szpak> <47BB30DF.1080006@student.tuwien.ac.at> <18364.6868.854623.613958@tree.ty.sabi.co.UK> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <18364.6868.854623.613958@tree.ty.sabi.co.UK> Sender: linux-raid-owner@vger.kernel.org To: Peter Grandi Cc: Linux RAID List-Id: linux-raid.ids Peter Grandi schrieb: > Those are as such not very meaningful. What matters most is > whether the starting physical address of each logical volume > extent is stripe aligned (and whether the filesystem makes use > of that) and then the stripe size of the parity RAID set, not > the chunk sizes in themselves. > > I am often surprised by how many people who use parity RAID > don't seem to realize the crucial importance of physical stripe > alignment, but I am getting used to it. Am I right to assume that stripe alignment matters because of the read-modify-write cycle needed for unaligned writes? If so, how come a pure read benchmark (hdparm -t or plain dd) is slower on the LVM device than on the md device? Oliver