Hi, Thanks for your advice, -----Original Message----- From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of Luis Periquito Sent: Friday, February 09, 2018 11:34 PM To: Kai Wagner Cc: Ceph Users Subject: Re: Newbie question: stretch ceph cluster On Fri, Feb 9, 2018 at 2:59 PM, Kai Wagner <kwagner@xxxxxxxx> wrote: > Hi and welcome, > > > On 09.02.2018 15:46, ST Wong (ITSC) wrote: > > Hi, I'm new to CEPH and got a task to setup CEPH with kind of DR feature. > We've 2 10Gb connected data centers in the same campus. I wonder if it's > possible to setup a CEPH cluster with following components in each > data > center: > > > 3 x mon + mds + mgr >>In this scenario you wouldn't be any better, as loosing a room means loosing half of your cluster. Can you run the MON somewhere else that would be able to continue if you loose one of the rooms? Will it be okay to have 3 x MON per DC so that we still have 3 x MON in case of losing 1 DC ? Or need more in case of double fault - losing 1 DC and failure of any MON in remaining DC will make the cluster stop working? >>As for MGR and MDS they're (recommended) active/passive; so one per room would be enough. > > 3 x OSD (replicated factor=2, between data center) >>replicated with size=2 is a bad idea. You can have size=4 and >>min_size=2 and have a crush map with rules something like: rule crosssite { id 0 type replicated min_size 4 max_size 4 step take default step choose firstn 2 type room step chooseleaf firstn 2 type host step emit } >>this will store 4 copies, 2 in different hosts and 2 different rooms. Does it mean for new data write to hostA:roomA, replication will take place as following? 1. from hostA:roomA to hostB:roomA 2. from hostA:roomA to hostA, roomB 3. from hostB:roomA to hostB, roomB If it works in this way, can copy in 3 be skipped so that for each piece of data, there are 3 replicas - original one, replica in same room, and replica in other room, in order to save some space? Besides, would also like to ask if it's correct that the cluster will continue to work (degraded) if one room is lost? Will there be any better way to setup such 'stretched' cluster between 2 DCs? They're extension instead of real DR site... Sorry for the newbie questions and we'll proceed to have more study and experiment on this. Thanks a lot. > > > So that any one of following failure won't affect the cluster's > operation and data availability: > > any one component in either data center failure of either one of the > data center > > > Is it possible? > > In general this is possible, but I would consider that replica=2 is > not a good idea. In case of a failure scenario or just maintenance and > one DC is powered off and just one single disk fails on the other DC, > this can already lead to data loss. My advice here would be, if anyhow > possible, please don't do replica=2. > > In case one data center failure case, seems replication can't occur any > more. Any CRUSH rule can achieve this purpose? > > > Sorry for the newbie question. > > > Thanks a lot. > > Regards > > /st wong > > > > > > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > > -- > SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, > HRB > 21284 (AG Nürnberg) > > > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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