Posted on Tue 30 April 2013

OpenStack Cinder - Add more volume nodes

With this being the first of a short series, I'd like to publish some articles intendend to cover the required steps to configure Cinder (OpenStack block storage service) in a mid/large deployment scenario. The idea is to discuss at least three topics: how to scale the service by adding more volume nodes; how to ensure high-availablity for the API and Scheduler sub-services; leverage the multi-backend feature landed in Grizzly.

I'm starting with this post on the scaling issue first. Cinder is composed of three main parts, the API server, the scheduler and the volume service. The volume service is some sort of abstraction layer between the API and the actual resources provider.

By adding more volume nodes into the environment you will be able to increase the total offering of block storage to the tenants. Each volume node can either provide volumes by allocating them locally or on a remote container like an NFS or GlusterFS share.

Some assumptions before getting into the practice:

  • you're familiar with the general OpenStack architecture
  • you have at least one Cinder node configured and working as expected

First thing to do on the candidate node is to install the required packages. I'm running the examples on CentOS and using the RDO repository which makes this step as simple as:

# yum install openstack-cinder

If you plan to host new volumes using the locally available storage dont' forget to create a volume group called cinder-volumes (the name can be configured via the cinder_volume parameter). Also don't forget to configure the tgtd to include the config files created dynamically by Cinder. Add a line like the following:

include /etc/cinder/volumes/*

in your /etc/tgt/targets.conf file. Now enable and start the tgtd service:

# chkconfig tgtd on
# service tgtd start

Amongst the three init services installed by openstack-cinder you only need to run openstack-cinder-volume, which gets configured in /etc/cinder/cinder.conf. Configure it to connect to the existing Cinder database (the db in use by the pre-existing node) and to the existing AMQP broker (again, in use by the pre-existing node) by setting the following:

sql_connection=mysql://cinder:${CINDER_DB_PASSWORD}@${CINDER_DB_HOST}/cinder
qpid_hostname=${QPIDD_BROKER}

Set the credentials if needed and/or change the rpc_backend setting if you're not using Qpid as your message broker. One more setting, not really required to change but worth checking if you're using the local resources:

iscsi_ip_address=${TGTD_IP_ADDRESS}

That should match the public ip address of the volume node just installed. The iSCSI targets created locally using tgtadm/tgtd have to be reachable by the Nova nodes. The IP address of each target is stored in the database with every volume created. The iscsi_ip_address prameter sets what is the IP address to be given to the initiators.

At this point you should be ready to start the volume service:

# service openstack-cinder-volume start

Verify that it started by checking the logs (/var/log/cinder/volume.log) or by issueing on any Cinder node:

# cinder-manage host list

you should see all of your volume nodes listed. From now on you can create new volumes as usual and they will be allocated on any of the volume nodes, keep in mind that the scheduler will default to the node with the most space available.

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