Cloud Storage Concepts — the “ceph” way — Part 2

Overview of Ceph Block Storage (RADOS) in OpenStack

Ceph is an open-source storage platform that provides unified storage solutions, including object, block, and file storage, all in one system. For OpenStack, Ceph Block Storage (via RADOS) is crucial because it offers high-performance, scalable storage that works perfectly for virtual machines (VMs) and databases. RADOS (Reliable Autonomic Distributed Object Store) is the backbone of Ceph and enables seamless data distribution, scalability, and fault tolerance.

The primary goal in deploying Ceph Block Storage is to ensure that virtual machine disks and databases benefit from distributed storage with automatic replication, self-healing, and efficient load balancing. Let’s dive into how this deployment is handled and how it integrates with OpenStack Cinder.

Deploying Ceph Block Storage (RADOS) in OpenStack

Deploying Ceph Cluster: First, a Ceph cluster is set up. This involves deploying Ceph monitors and OSDs (Object Storage Daemons) that form the backbone of the storage system. Monitors manage the overall state of the cluster, while OSDs handle data storage and replication.

Sample Code to Deploy Ceph OSD Nodes:

ceph-deploy new node1 node2 node3  # Create a new Ceph cluster with 3 nodes
ceph-deploy install node1 node2 node3  # Install Ceph on all nodes
ceph-deploy mon create-initial  # Create initial monitor for cluster
ceph-deploy osd prepare node1:/dev/sdb node2:/dev/sdb node3:/dev/sdb  # Prepare OSD disks
ceph-deploy osd activate node1:/dev/sdb node2:/dev/sdb node3:/dev/sdb  # Activate OSDs

Step-by-Step Breakdown of a Ceph Deployment

ceph-deploy new node1 node2 node3 - Creating a New Ceph Cluster

The very first step in deploying Ceph is to create the cluster. Here, ceph-deploy is used to initialize a new Ceph cluster that spans three nodes (node1, node2, and node3). This command sets the foundation for the cluster, configuring each node to participate in the Ceph storage system.

What Happens:

• ceph-deploy sets up the initial configuration file (ceph.conf) for the cluster. This file includes details about the cluster such as the monitors (nodes that manage the health of the cluster) and the overall topology.
• This command lays down the structure for communication between the nodes and prepares them to serve different roles (as monitors or OSD nodes).

ceph-deploy install node1 node2 node3 - Installing Ceph on All Nodes

Once the cluster is defined, the next step is to install Ceph on each node. This command automates the installation process, ensuring that each node has the necessary Ceph binaries, libraries, and dependencies.

What Happens:

• ceph-deploy uses package management systems (like apt for Ubuntu or yum for CentOS) to install Ceph on all the nodes. It ensures that the version of Ceph is consistent across the entire cluster.
• This step is crucial for maintaining a uniform deployment. It also includes important utilities such as ceph-mon, ceph-osd, and ceph-mgr, which manage different aspects of the cluster.

Sample Output:

[node1][INFO] installing ceph on node1
[node2][INFO] installing ceph on node2
[node3][INFO] installing ceph on node3

ceph-deploy mon create-initial - Creating the Initial Monitor for the Cluster

The next command sets up the monitor service, which is essential for the cluster’s operation. Ceph monitors (MONs) maintain the cluster map, ensuring all nodes are aware of the cluster’s current state.

What Happens:

• The ceph-deploy tool configures the first monitor on one of the nodes (usually the primary node) and sets it up as the initial monitor for the cluster.
• A monitor handles critical cluster information such as which OSDs are available and which nodes are healthy. It essentially acts as the brain of the Ceph cluster, overseeing cluster health and ensuring that data is correctly distributed.

Sample Output:

[node1][INFO] monitor creation successful

ceph-deploy osd prepare node1:/dev/sdb node2:/dev/sdb node3:/dev/sdb - Preparing OSDs

Object Storage Daemons (OSDs) are the workhorses of the Ceph cluster. They handle the actual storage of data and are responsible for replicating, rebalancing, and recovering data across the cluster. This command prepares the hard drives on each node to be used as OSDs.

What Happens:

• The osd prepare command formats the storage devices (/dev/sdb in this case) on each node and prepares them to be added as OSDs in the cluster.
• The storage devices are divided into the necessary partitions and metadata structures required by Ceph to manage the data placement and redundancy efficiently.

Sample Output:

[node1][INFO] OSD prepared on /dev/sdb
[node2][INFO] OSD prepared on /dev/sdb
[node3][INFO] OSD prepared on /dev/sdb

ceph-deploy osd activate node1:/dev/sdb node2:/dev/sdb node3:/dev/sdb - Activating the OSDs

After preparing the OSDs, they need to be activated. This step registers the OSDs with the Ceph cluster, making them available for use.

What Happens:

• The activation process ensures that the OSDs are brought online and integrated into the Ceph cluster. The Ceph monitors (configured earlier) now recognize the OSDs and start distributing data across them.
• Once activated, the OSDs can handle read and write operations, data replication, and failover operations as necessary.

Sample Output:

[node1][INFO] OSD activated on /dev/sdb
[node2][INFO] OSD activated on /dev/sdb
[node3][INFO] OSD activated on /dev/sdb

These commands create the backbone of a Ceph storage cluster. In this example:

• We initialized a Ceph cluster across three nodes.
• We installed Ceph on those nodes.
• We set up the initial monitor to manage the cluster’s state.
• Finally, we prepared and activated the OSDs, enabling the cluster to store data.

Each step in this process ensures that the Ceph cluster is highly available, scalable, and fault-tolerant. Ceph’s self-healing capabilities and dynamic rebalancing make it an excellent choice for modern, distributed storage needs. Whether you’re deploying Ceph for virtual machine storage in OpenStack or managing a petabyte-scale object storage system, the ceph-deploy tool simplifies the process, allowing engineers to focus more on performance tuning and scaling rather than low-level configuration tasks

Configuring Ceph for Block Storage (RADOS): Once the Ceph cluster is up, we configure it to handle block storage. Ceph RBD is a feature that allows us to create block devices from the Ceph storage pool. These block devices can be used as virtual machine disks or for databases that need high throughput and reliability.

Creating a Pool for Block Storage:

ceph osd pool create rbd 128 128  # Create a pool named "rbd" with 128 placement groups
rbd pool init rbd  # Initialize the pool for RBD usage

Integrating Ceph RBD with OpenStack Cinder

To fully integrate Ceph Block Storage into an OpenStack environment, we need to connect Ceph RBD with OpenStack’s block storage service, Cinder. This integration allows OpenStack users to provision and manage Ceph block devices directly through the OpenStack interface, offering seamless storage scaling and management.

Configuring Cinder to Use Ceph RBD: We modify the Cinder configuration file to point to our Ceph cluster, ensuring that it can create and manage RBD volumes.

Cinder Configuration for Ceph RBD (/etc/cinder/cinder.conf):

[DEFAULT]
enabled_backends = ceph

[ceph]
volume_driver = cinder.volume.drivers.rbd.RBDDriver
rbd_pool = rbd  # The Ceph pool used for block storage
rbd_ceph_conf = /etc/ceph/ceph.conf
rbd_user = cinder
volume_backend_name = ceph

Ensuring Data Redundancy and Fault Tolerance: Ceph automatically replicates block storage data across multiple OSD nodes, ensuring that even if one node fails, the data is available from other nodes. This replication is configured at the pool level, and by default, Ceph uses 3x replication, meaning every piece of data is stored on three different OSDs.

Setting the Replication Level:

ceph osd pool set rbd size 3  # Set replication size to 3

Provisioning Block Storage in OpenStack: Once the integration is complete, users can provision block storage directly from OpenStack, and the Ceph RBD will handle the back-end storage automatically. Virtual machine disks, databases, and other high-performance applications can now benefit from Ceph’s distributed architecture.

Sample Code for Creating a Volume in OpenStack:

openstack volume create --size 10 ceph_volume  # Creates a 10GB volume on Ceph via Cinder

Automating Ceph Block Storage Provisioning with Ansible and Terraform

One of the most effective ways to manage block storage provisioning is to automate the process. By using tools like Ansible and Terraform, manual configurations that can often introduce errors are minimized, leading to faster and more efficient deployments across both private and hybrid cloud environments.

Using Ansible Playbooks for Block Storage Automation:
Ansible is a powerful automation tool that allows for infrastructure management through simple, human-readable playbooks. In this scenario, I created an Ansible playbook to automate the provisioning of Ceph RBD (RADOS Block Device) pools. The playbook ensures that each step — pool creation, OSD node setup, and RBD configuration — is executed consistently and efficiently.

Sample Ansible Playbook:

- hosts: storage_nodes
  become: yes
  tasks:
    - name: Create RBD pool
      command: ceph osd pool create rbd_pool 128 128
    - name: Initialize RBD pool
      command: rbd pool init rbd_pool
    - name: Add OSD nodes
      command: ceph-deploy osd create --data /dev/sdb {{ inventory_hostname }}

In this playbook, we first create a Ceph RBD pool, initialize it, and then add Object Storage Daemon (OSD) nodes. The playbook ensures that each task is executed consistently across all nodes, reducing manual errors.

Integrating Terraform for Hybrid Cloud Deployments:
Terraform is another essential tool that allows for the management of infrastructure as code. By using Terraform alongside Ansible, we can ensure that the provisioning of Ceph block storage can extend beyond private clouds to hybrid environments, integrating public cloud resources like AWS or Azure.

Sample Terraform Code for Ceph Cluster Provisioning:

resource "aws_instance" "ceph_nodes" {
  count         = 3
  ami           = "ami-0c55b159cbfafe1f0" # Amazon Linux 2 AMI
  instance_type = "t2.medium"
  tags = {
    Name = "CephNode-${count.index}"
  }
}

resource "null_resource" "setup_ceph" {
  provisioner "local-exec" {
    command = "ansible-playbook -i inventory.yml ceph-playbook.yml"
  }
}

Configuring Ceph’s Self-Healing and Auto-Scaling Features

Ceph’s built-in self-healing and auto-scaling mechanisms are key features that ensure data reliability and high availability. These features allow the system to automatically detect failed nodes and redistribute data across healthy nodes, ensuring uninterrupted access to data.

Self-Healing:
Ceph’s self-healing capabilities are powered by its CRUSH algorithm, which dynamically distributes data across OSDs. If an OSD fails, Ceph automatically re-replicates the lost data to other healthy nodes.

Command to Enable Self-Healing:

ceph osd set norebalance
ceph osd set backfillfull_ratio 0.85

This ensures that the cluster is ready to backfill missing data as soon as an OSD fails.

Auto-Scaling:
Ceph can dynamically scale storage by adding more OSDs. When new storage nodes are added, Ceph automatically rebalances the data to maintain even distribution across the cluster.

Command to Add New OSD:

ceph-deploy osd create --data /dev/sdc new_node

Custom Python Scripts for Monitoring and Maintenance

To maintain optimal performance in the Ceph cluster, I developed custom Python scripts to monitor key metrics such as disk usage, IOPS, and latency. These scripts also help automate maintenance tasks, such as node addition and cluster rebalancing.

Sample Python Script for Monitoring Ceph Cluster:

import rados

# Connect to Ceph cluster
cluster = rados.Rados(conffile='/etc/ceph/ceph.conf')
cluster.connect()

# Fetch and display cluster stats
stats = cluster.get_cluster_stats()
print(f"Cluster Usage: {stats['kb_used'] / 1024 / 1024} GB used")

This script connects to the Ceph cluster and retrieves real-time statistics, providing insights into how the cluster is performing. Regular monitoring helps identify potential bottlenecks and ensures that the system remains healthy.

By automating the provisioning of block storage using Ansible and Terraform, and configuring Ceph’s self-healing and auto-scaling features, we ensure a highly reliable and scalable storage solution. Custom Python scripts further enhance the system’s maintainability by providing real-time performance insights and automating routine tasks. This combination of automation, dynamic scaling, and monitoring creates a robust Ceph storage infrastructure that meets the demanding needs of private and hybrid cloud environments.