From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gionatan Danti Subject: Re: RAID 10 far and offset on-disk layouts Date: Tue, 14 Jan 2014 10:27:12 +0100 Message-ID: <52D502F0.2090703@assyoma.it> References: <52BD8EDD.10809@assyoma.it> <20131227151927.GA4003@www5.open-std.org> <52BD9B4F.3000509@assyoma.it> <20131227154952.GA6539@www5.open-std.org> <52CE57D9.1030501@assyoma.it> <20140113102021.1ef3e203@notabene.brown> <52D3A962.4000308@assyoma.it> <20140113204534.737a98f6@notabene.brown> <52D3BCB1.1010200@assyoma.it> <20140114092751.09464b7b@notabene.brown> <52D4FE05.3020709@assyoma.it> <20140114201655.61f4e10b@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140114201655.61f4e10b@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: NeilBrown Cc: linux-raid@vger.kernel.org, keld@keldix.com, Gionatan Danti List-Id: linux-raid.ids >> Ok, so let recap: >> >> 1) FAR layout is the one depicted by SuSe documentation, while the >> Wikipedia entry is wrong > > Yes. > >> >> 2) MD _can_ produce a FAR layout as depicted by Wikipedia, but we don't >> know how the user-space mdadm tool call it (maybe it is not implemented >> yet?) > > Yes. Not implemented yet. > >> >> 3) There are any reasons why FAR and OFFSET layout scramble data in this >> manner, coupling any disk with two more disks? It was done for >> simplicity, or I am missing something? > > It just seemed the easiest thing to do at the time. > >> >> 4) you confirm that currently we can _not_ create a FAR layout as the >> one depicted by wikipedia by no means? What about OFFSET layout? > > You certainly can created the FAR layout depicted on wikipedia, e.g. by > binary-editing the metadata on some devices, or writing some code which does > that for you. It requires flipping one bit in the metadata and updating the > checksum. You can probably even to it by writing something appropriate into > some sysfs files. > But mdadm cannot do it yet. > Ditto for the new OFFSET layout. > (The old offset layout can be created with "--layout=o2"). > > NeilBrown > All clear now :) Thank you very much Neil. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8