what is the point of CEPH, if there is no HA?

[jpv31]

Hello,

I use proxmox regularly and I think I have understood how it works, except what happens if CEPH is installed without HA.

We have a cluster of 3 servers.

CEPH is installed on each of the servers, and we have defined OSD and POOLS, with replication on the 3 servers.

If HA is installed and correctly configured, and for example if node n°1 fails, the virtual machines running on node n°1 will migrate and automatically start on nodes n°2 and n°3.

So far it’s clear!

Now if there is no HA and node n°1 goes down, what will happen?

The VMs from node n°1 will not automatically migrate and start on node n°2 and 3.

In this case what is the point of CEPH, if there is no HA?

Will the VMs which were on node n° 1 will migrate, without starting automatically, on nodes n° 2 and n° 3 ?

Will it nevertheless be possible to start manually on ?

Thank you in advance for your clarifications!
Best regards

 

[sterzy]

The VMs from node n°1 will not automatically migrate and start on node n°2 and 3.

No, they won't be restarted automatically, that would be the point of HA. So if you don't use HA for your guests, they won't be restarted automatically.

In this case what is the point of CEPH, if there is no HA?

You still have a distributed file system with redundancy. So you can manually restart the VMs without starting the missing node again. It also allows you do to do maintenance more easily without having to migrate the guest's storage to another node's local storage. Also Ceph provides redundancy if set up properly, so the loss of a node shouldn't result in the loss data.

Will the VMs which were on node n° 1 will migrate, without starting automatically, on nodes n° 2 and n° 3 ?

They won't start automatically. You'd need to migrate them yourself and then restart them. This should be doable since their storage is on CEPH and not local to node 1.

Will it nevertheless be possible to start manually on ?

Yes.