Deploying Ceph monitor nodes using host labels

A typical IBM Storage Ceph storage cluster has three or five Ceph Monitor daemons deployed on different hosts. If your storage cluster has five or more hosts, deploy five Ceph Monitor nodes. Use host labels to identify the hosts that contain Ceph Monitor nodes.

If your Ceph Monitor nodes or your entire cluster are located on a single subnet, then cephadm automatically adds up to five Ceph Monitor daemons as you add new nodes to the cluster. cephadm automatically configures the Ceph Monitor daemons on the new nodes. The new nodes reside on the same subnet as the first (bootstrap) node in the storage cluster. cephadm can also deploy and scale monitors to correspond to changes in the size of the storage cluster.

Prerequisites

Before you begin, make sure that you have the following prerequisites in place:

Root-level access to all nodes in the storage cluster.
A running storage cluster.

Procedure

Assign the mon label to the host:

Syntax

ceph orch host label add HOSTNAME mon

Example

[ceph: root@host01 /]# ceph orch host label add host02 mon
[ceph: root@host01 /]# ceph orch host label add host03 mon

View the current hosts and labels:

Syntax

ceph orch host ls

Example

[ceph: root@host01 /]# ceph orch host ls
HOST   ADDR   LABELS  STATUS
host01        mon,mgr,_admin
host02        mon
host03        mon
host04
host05
host06

Deploy Ceph Monitor daemons based on the host label:

Syntax
```
ceph orch apply mon label:mon
```
Deploy Ceph Monitor daemons on a specific set of hosts:

Syntax
```
ceph orch apply mon HOSTNAME1,HOSTNAME2,HOSTNAME3
```
Example
```
[ceph: root@host01 /]# ceph orch apply mon host01,host02,host03
```
Note: Be sure to include the bootstrap node in the list of hosts to which you want to deploy.