Hello Franck, it's not an easy question to answer, I'll just write up a few of my thoughts. In general, ceph is a good idea for openstack, yes. But you have to keep in mind that when a server fails in a 3 node cluster it becomes degraded as there's no target for recovery left until the server comes back online. So my recommendation would be at least 4 nodes for a "real" production ceph cluster, but 3 would work as long as your infrastructure is stable enough (no regular power outages or anything). Colocating ceph and openstack on the same hardware can work (I read about it once in a while), but that means more services become unavailable (or are degraded) in case of maintenance or failure. And I'm not sure how deployment tools like kolla-ansible deal with it, I've never installed such a mixed infrastructure. If you colocated the compute service with the ceph servers you would have to migrate VMs every time a ceph server needs maintenance, or they become unavailable if a server fails unexpectedly (and you'd have to tweak the database to migrate them to a different compute node). So from a maintenance/failure point of view colocation is not the best idea. We've had a single control node openstack running for years without any incident, but updating was disruptive, of course, at least for self-service networks, provider networks are directly available on the compute nodes, so most of the infrastructure was not impacted. We then added a second control node with a galera tie-breaker to have a HA cluster. The question is what your requirements actually are wrt (high) availability. How is your current setup with 3 nodes? Are all 3 nodes both control and compute nodes? What is the current storage backend, local filesystem of the compute nodes? Is it an option to buy more (smaller) nodes so that you could have a dedicated ceph cluster? Regards, Eugen Zitat von Franck VEDEL <franck.vedel@univ-grenoble-alpes.fr>:
Good morning, I currently have an Openstack cluster made up of 3 nodes, an iscsi bay (10T), 576 G of Ram, 10T, 288vcpus. This cluster is used by around 150 students, but is reaching its limits. Having obtained a budget to set up a larger cluster, I am wondering about the choice of the number of nodes, their role (how many controllers, network, compute, etc.) and above all what solution for storage. Let's imagine a budget to buy 6 servers with good capacities, is the right choice Ceph storage (with cinder and rdb?) on the Openstack cluster nodes? Do we need 3 servers for a Ceph cluster and 3 for the Openstack part (in this case I lose capacity for the "compute" part)... I don't know what the right choices are and above all, I have a little afraid of going in the wrong directions. Could any of you guide me, or give me links to sites that could help me (and that I haven't seen). Thanks in advance
Franck VEDEL Dép. Réseaux Informatiques & Télécoms IUT1 - Univ GRENOBLE Alpes 0476824462 Stages, Alternance, Emploi.