I'm a n00b myself, but I'll go on record with my understanding. On Sun, Jun 4, 2017 at 3:03 PM Benoit GEORGELIN - yulPa < benoit.george...@yulpa.io> wrote:
> Hi ceph users, > > Ceph have a very good documentation about technical usage, but there is a > lot of conceptual things missing (from my point of view) > It's not easy to understand all at the same time, but yes, little by > little it's working. > > Here are some questions about ceph , hope someone can take a little time > to point me where I can find answers : > > - Backup : > Do you backup data from a CEPH cluster or you consider a copy as a backup > of that file ? > Let's say I have replica size of 3 . Somehow , my crush map will keep 2 > copy in my main rack and 1 copy to another rack in another datacenter > Can I consider the third copy as a backup ? What would be your position ? > Replicas are not backups. Just ask GitLab after accidental deletion. source: https://www.theregister.co.uk/2017/02/01/gitlab_data_loss/ > - Writing process of ceph object storage using radosgw > Simple question, but not sure about it. > The more replica the more slower will be my cluster ? Does CEPH have to > acknowledge the number of replica before saying it's good ? > From what I read, CEPH will write and acknowledge the de primary OSD of > the pool , So if that the cas, I does not matter how many replica I want > and how far are situated the others OSD that would work the same. > Can I chose myseft the primary OSD in my zone 1 , have a copy on zone 2 > (same rack) and a third zone 3 in another datacenter that might have some > latency . > More replicas make slower cluster because it waits for all devices to acknowledge write before reporting back. source: ? > - Data persistance / availability > If crush map is by hosts and I have 3 hosts with replication of 3 > This means , I will have 1 copy on each hosts > Does it means I can lost 2 hosts and still have my cluster working, at > least on read mode ? and eventually in write too if i say , osd pool > default min size = 1 > Yes, I think. But best practice is to have at least 5 hosts (N+2) so you can lose 2 hosts and still keep 3 replicas. > > Thanks for your help. > - > > Benoît G > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com Roger
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