From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gionatan Danti Subject: Re: RAID 10 far and offset on-disk layouts Date: Fri, 27 Dec 2013 18:32:48 +0100 Message-ID: <52BDB9C0.2020906@assyoma.it> References: <52BD8EDD.10809@assyoma.it> <52BD99BC.8000205@assyoma.it> <21181.46549.590241.76206@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: <21181.46549.590241.76206@tree.ty.sabi.co.uk> Sender: linux-raid-owner@vger.kernel.org To: Peter Grandi , Linux RAID List-Id: linux-raid.ids > > Therefore the *probability* of loss of data because of 2 member > devices failing is higher in layout 1) than layout 2), whether > or not the drives are "adjacent". > > Note that arguably layout 1) is not really RAID10, because an > important property of RAID10 is or should be that there are > only N/2 pairs out of N drives. Otherwise it is not quite > 'RAID1' if a chunk position in a stripe can be replicated on 2 > other devices, half the replicas on one and half on another. > > That the member devices are *adjacent* is irrelevant; what > matters is the statistical chance, which is driven by the > percent of cases where 2 failures result in data loss, which > driven by the number of paired drives. Very detailed answer, thank you Peter :) Based on what keld told before, the current scheme if n.2 (wikipedia's one), right? It is possible, using mdadm, understand the physical layout (if n.1 or n.2) of a live RAID10 array? As schema n.1 lead to increased probability of data loss, why offset layout use it instead of, say, some variance of schema n.2? Regards. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8