From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christina Braun Subject: Re: direction criterium for synchronisation raid1 Date: Tue, 16 Oct 2007 15:32:58 +0200 Message-ID: <4714BD8A.8000307@mail.informatik.uni-essen.de> References: <47148439.2020706@mail.informatik.uni-essen.de> Reply-To: braun@dc.uni-due.de Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Thank you very much for your quick and detailed elaboration! That is my searched answer and more. I have made a short test for quick looking at the event-counters with my testpartitions. I failed and removed the local mirror-leg and keep the remaining active iscsi-leg on the other server (I use raid1 with iscsi on 2 servers), copied some files to the md, added then the removed local partition again. I watched the counters in all phases and can see the differences and after syncing the same counters. The criterion event-counter removes also my little doubt about using iscsi-raid1. Also I am very glad for your advice in case of mounting md-devices as plain-filesystems and remaining older data in relationship of this counter. I will now pay great attention to this event-counter :-) Best regards, Christina Mario 'BitKoenig' Holbe schrieb: > Christina Braun wrote: > >> which is in raid1 the criterion for the direction of synchronisation? In >> > > The event counter :) > > >> How can I tell the system which mirrored partition is now the >> data-source without >> making the raid1 new or zero the superblock? Is the destination in >> > > Usually you don't need to do this. md manages a per-mirror event counter > which always gets increased when relevant events occur like assembling > or stopping an array, adding or removing mirrors etc. > Due to this, whenever you remove a mirror off an raid1, the event > counter of the remaining mirrors gets increased. When you shut down your > machine, plug a disk off and turn the machine on again, once the raid > gets assembled, the event counter of the remaining mirrors gets > increased. > > Thus, as long as you access those devices through md only (and don't > mount the device of one of the mirrors as plain filesystem, for > example), the remaining mirrors will always be newer than removed ones > and thus md knows the sync-direction (when they are equally "old", they > are in sync per definition). > > There are some exceptions to this: > 1. When you like to use the older mirror as source of synchronization, > you have to take care and better zero the superblock of the newer one > before (make sure your raid device did not get assembled, probably based > on the wrong mirror). > 2. When you plug a foreign mirror into the system which - however - > refers to the same raid-device (especially having the same UUID etc.) > as your own mirrors but has a bigger event counter, you have to take > care a lot :) This should usually not happen accidentially, as long as > you avoid to assign UUIDs to new raids manually. > > >> every case the device >> in mdadm manage after the add ? Can I see the source or destination by a >> info like mdstat or superblock? >> > > Have a look at mdadm -E. This shows you the superblocks of single > mirrors and within them their respective event counters. > > > regards > Mario > -- ********************************************** /\_/\ * email: braun@dc.uni-due.de / 0 0 \ * Christina Braun ====v==== * FB. 5, ICB / Informatik \ W / * University DE | | * Schuetzenbahn 70 tel.: + 49 201 183-3929 / ___ \ / * D-45127 Essen fax.: + 49 201 183-2419 / / \ \ | **********************************************(((-----)))-'