From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Greaves Subject: Re: raid5/lvm setup questions Date: Mon, 07 Aug 2006 23:28:46 +0100 Message-ID: <44D7BE9E.6020807@dgreaves.com> References: <20060805165358.GA29177@cm.nu> <44D4D5F9.9080201@dgreaves.com> <87mzagz5d2.fsf@hades.wkstn.nix> <20060807200455.GA29837@cm.nu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20060807200455.GA29837@cm.nu> Sender: linux-raid-owner@vger.kernel.org To: Shane Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Shane wrote: > On Mon, Aug 07, 2006 at 08:57:13PM +0100, Nix wrote: >> On 5 Aug 2006, David Greaves prattled cheerily: >>> As an example of the cons: I've just set up lvm2 over my raid5 and whilst >>> testing snapshots, the first thing that happened was a kernel BUG and an oops... >> I've been backing up using writable snapshots on LVM2 over RAID-5 for >> some time. No BUGs. > > Just performed some basic throughput tests using 4 SATA > disks in a raid5 array. The read performance on the > /dev/mdx device runs around 180mbps but if lvm is layered > over that, reads on the lv are around 130mbps. Not an > unsubstantial reduction. Check the readahead at various block levels blockdev --setra xxx I think I found the best throughput (for me) was with 0 readahead for /dev/hdX, 0 for /dev/mdX and lots for /dev/vg/lv > > I seem to recall patches to md floating around a couple > years back for partitioning of md devices. Are those still > available somewhere? man mdadm and see --auto... David --