Ceph is a massively scalable, open source, distributed storage system. Ceph is in the Linux kernel and is integrated with the OpenStack cloud operating system.
Three parts of OpenStack integrate with Ceph’s block devices:
- Images: OpenStack Glance manages images for VMs. Images are immutable. OpenStack treats images as binary blobs and downloads them accordingly.
- Volumes: Volumes are block devices. OpenStack uses volumes to boot VMs, or to attach volumes to running VMs. OpenStack manages volumes using Cinder services.
- Guest Disks: Guest disks are guest operating system disks. By default, when you boot a virtual machine, its disk appears as a file on the filesystem of the hypervisor (usually under/var/lib/nova/instances/<uuid>/). Prior to OpenStack Havana, the only way to boot a VM in Ceph was to use the boot-from-volume functionality of Cinder. However, now it is possible to boot every virtual machine inside Ceph directly without using Cinder, which is advantageous because it allows you to perform maintenance operations easily with the live-migration process. Additionally, if your hypervisor dies it is also convenient to trigger nova evacuate and run the virtual machine elsewhere almost seamlessly.
You can configure the Compute service to use Ceph RADOS block devices (RBD) for volumes and due to its open-source nature, you can install and use this portable storage platform in public or private clouds. The platform can auto-scale to the exabyte level and beyond. It runs on commodity hardware, is self-healing and self-managing, and has no single point of failure.
HOW IT WORKS
Ceph RBD interfaces with the same Ceph object storage system that provides the librados interface and the Ceph FS file system, and it stores block device images as objects. Since RBD is built on top of librados, RBD inherits librados capabilites, including read-only snapshots and revert to snapshot. By striping images across the cluster, Ceph improves read access performance for large block device images.
- Thinly provisioned
- Resizable images
- Image import/export
- Image copy or rename
- Read-only snapshots
- Revert to snapshots
- Ability to mount with Linux or QEMU KVM clients!
Ceph is based on Reliable Autonomic Distributed Object Store (RADOS). It’s a storage systems that distributes objects across the storage cluster and replicates objects for fault tolerance. Use as an object, default storage mechanism.
Pictures from OpenStack.org