Chapter 2. Ceph network configuration

Network configuration is critical for building a high performance Red Hat Ceph Storage cluster. The Ceph storage cluster does not perform request routing or dispatching on behalf of the Ceph client. Instead, Ceph clients make requests directly to Ceph OSD daemons. Ceph OSDs perform data replication on behalf of Ceph clients, which means replication and other factors impose additional loads on the networks of Ceph storage clusters.

All Ceph clusters must use a public network. However, unless you specify an internal cluster network, Ceph assumes a single public network. Ceph can function with a public network only, but for large storage clusters you will see significant performance improvement with a second private network for carrying only cluster-related traffic.

To support two networks, each Ceph Node will need to have more than one network interface card (NIC).

There are several reasons to consider operating two separate networks:

Network configuration settings are not required. Ceph can function with a public network only, assuming a public network is configured on all hosts running a Ceph daemon. However, Ceph allows you to establish much more specific criteria, including multiple IP networks and subnet masks for your public network. You can also establish a separate cluster network to handle OSD heartbeat, object replication, and recovery traffic.

Do not confuse the IP addresses you set in the configuration with the public-facing IP addresses network clients might use to access your service. Typical internal IP networks are often 192.168.0.0 or 10.0.0.0.

When you configured the networks, you can restart the cluster or restart each daemon. Ceph daemons bind dynamically, so you do not have to restart the entire cluster at once if you change the network configuration.

Ceph has one network configuration requirement that applies to all daemons. The Ceph configuration file must specify the host for each daemon.

You can set the host names and the IP addresses for where the daemon resides by specifying the host name.

[mon.a]
    host = host01
    mon_addr = 10.0.0.101:6789, 10.0.0.101:3300

[osd.0]
    host = host02

You do not have to set the node IP address for a daemon, it is optional. If you have a static IP configuration and both public and private networks running, the Ceph configuration file might specify the IP address of the node for each daemon. Setting a static IP address for a daemon must appear in the daemon instance sections of the Ceph configuration file.

[osd.0]
    public_addr = 10.74.250.101/21
    cluster_addr = 10.74.250.101/21

You can deploy an OSD host with a single NIC in a cluster with two networks by forcing the OSD host. You can force the OSD host to operate on the public network by adding a public addr entry to the [osd.n] section of the Ceph configuration file, where n refers to the number of the OSD with one NIC. Additionally, the public network and cluster network must be able to route traffic to each other, which Red Hat does not recommend for security reasons.

Messenger is the Ceph network layer implementation. Red Hat supports two messenger types:

In Red Hat Ceph Storage 3 and higher, async is the default messenger type. To change the messenger type, specify the ms_type configuration setting in the [global] section of the Ceph configuration file.

The public network configuration allows you specifically define IP addresses and subnets for the public network. You may specifically assign static IP addresses or override public network settings using the public addr setting for a specific daemon.

[global]
    ...
    public_network = PUBLIC-NET/NETMASK

If you declare a cluster network, OSDs will route heartbeat, object replication, and recovery traffic over the cluster network. This can improve performance compared to using a single network.

The cluster network configuration allows you to declare a cluster network, and specifically define IP addresses and subnets for the cluster network. You can specifically assign static IP addresses or override cluster network settings using the cluster addr setting for specific OSD daemons.

[global]
    ...
    cluster_network = CLUSTER-NET/NETMASK

By default, daemons bind to ports within the 6800:7100 range. You can configure this range at your discretion. Before configuring the firewall, check the default firewall configuration.

Ceph monitors listen on port 3300 and 6789 by default. Additionally, Ceph monitors always operate on the public network.

By default, Ceph OSDs bind to the first available ports on a Ceph node beginning at port 6800. Ensure to open at least four ports beginning at port 6800 for each OSD that runs on the node:

Ports are node-specific. However, you might need to open more ports than the number of ports needed by Ceph daemons running on that Ceph node in the event that processes get restarted and the bound ports do not get released. Consider to open a few additional ports in case a daemon fails and restarts without releasing the port such that the restarted daemon binds to a new port. Also, consider opening the port range of 6800:7300 on each OSD node.

If you set separate public and cluster networks, you must add rules for both the public network and the cluster network, because clients will connect using the public network and other Ceph OSD Daemons will connect using the cluster network.

If you put the cluster network into another zone, open the ports within that zone as appropriate.

The maximum transmission unit (MTU) value is the size, in bytes, of the largest packet sent on the link layer. The default MTU value is 1500 bytes. Red Hat recommends using jumbo frames, a MTU value of 9000 bytes, for a Red Hat Ceph Storage cluster.