Re: How are replicas spread in default crush configuration?

[Chris Taylor <ctaylor@xxxxxxxxxx>]

Kevin,

After changing the pool size to 3, make sure the min_size is set to 1 to allow 2 of the 3 hosts to be offline.

http://docs.ceph.com/docs/master/rados/operations/pools/#set-pool-values

How many MONs do you have and are they on the same OSD hosts? If you have 3 MONs running on the OSD hosts and two go offline, you will not have a quorum of MONs and I/O will be blocked.

I would also check your CRUSH map. I believe you want to make sure your rules have "step chooseleaf firstn 0 type host" and not "... type osd" so that replicas are on different hosts. I have not had to make that change before so you will want to read up on it first. Don't take my word for it.

http://docs.ceph.com/docs/master/rados/operations/crush-map/#crush-map-parameters

Hope that helps.

 

Chris

 

On 2016-11-23 1:32 pm, Kevin Olbrich wrote:

Hi,

 

just to make sure, as I did not find a reference in the docs:

Are replicas spread across hosts or "just" OSDs?

 

I am using a 5 OSD cluster (4 pools, 128 pgs each) with size = 2. Currently each OSD is a ZFS backed storage array.

Now I installed a server which is planned to host 4x OSDs (and setting size to 3).

 

I want to make sure we can resist two offline hosts (in terms of hardware).

Is my assumption correct?

Mit freundlichen Grüßen / best regards,
Kevin Olbrich.

_______________________________________________
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