From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keld =?iso-8859-1?Q?J=F8rn?= Simonsen Subject: Re: raid-0 with mdadm vs lvm striping Date: Thu, 13 Aug 2009 10:08:34 +0200 Message-ID: <20090813080834.GA24883@rap.rap.dk> References: <3ECBDC05781B3D48ABD520A01ABF2F9B2E99EDBB63@SE-EX008.groupinfra.com> <3ECBDC05781B3D48ABD520A01ABF2F9B2E9A0485D5@SE-EX008.groupinfra.com> <87vdkt4e5x.fsf@frosties.localdomain> <3ECBDC05781B3D48ABD520A01ABF2F9B2E9A048A82@SE-EX008.groupinfra.com> <874osc5ut5.fsf@frosties.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <874osc5ut5.fsf@frosties.localdomain> Sender: linux-raid-owner@vger.kernel.org To: Goswin von Brederlow Cc: Billy Crook , "Henry, Andrew" , Drew , "linux-raid@vger.kernel.org" List-Id: linux-raid.ids On Thu, Aug 13, 2009 at 04:09:10AM +0200, Goswin von Brederlow wrote: > Billy Crook writes: >=20 > > On Wed, Aug 12, 2009 at 04:14, Henry, Andrew wrote: > >> That's what my question was: =A0Will raid0 (striping) be faster or= easier to manage than lvm striping > > > > LVM striping won't change performance for small files. (That is fil= es, > > smaller than the extent size.) To be fair, RAID-0 striping won't > > accelerate file access for files smaller than the stripe size eithe= r. Have you tested this? In theory, both LVM and raid0 striping should accellerate access to small files substantially, for example if a process accesses a number of small files, which are laid out in sequenc= e on the file system. This is a common case.=20 I think this could come about eg if you roll in a tarball or package of a system, then the small files are created in sequence, and the file system should lay them out in sequence on the disk. When reading again, the disk read ahead would secure that most of the data for a number of small files were already read into the kernel cache when asked for, and thus the files would be read at striping speeds.=20 > > However, traditionally, raid0 stripe sizes are much much smaller th= an > > LVM extent sizes. Both are however adjustable. What are the parameters? raid normally assumes 64 kiB chunks, but i normally use 256 kiB chunks, which is the lowest chunk size that we are recommending out of the linux-raid group. What are normal with LVM? best regards keld -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html