openstack ceph concept

asked 2020-06-16 01:34:05 -0600

happy75 gravatar image

HI Openstack ceph experts, For those of you who knows openstack ceph - can you please clarify the following for me: - Ceph is known as the unified storage solution (i.e. file, block and object storage) - what does that really mean? Does that mean you can create files (file storage), volumes (block storage like cinder) or objects (object storage like swift) in ceph? If you are only using ceph as file storage, are the files still stored as objects inside RADOS? Likewise if you use it as block storage, does that mean the volumes are stored as block in RADOS but appear to the application as volumes (blocks)? I haven't actually installed ceph yet but do you actually get an option on whether you want create file system or volumes or objects under the ceph menu? I am doing some research on the internet but if somebody can explain this to me, that would be great. thanks in advance!

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answered 2020-06-16 02:04:00 -0600

eblock gravatar image

Basically, all stored data in ceph is stored as rados objects, independent of the application you're using (CephFS, RGW, RBD). For OpenStack you typically use RBD (Rados Block Device) which appear as block devices to the clients (instances), but they are still stored as many objects within ceph. That's how ceph scales up: many different objects of the same rbd can be queried on different OSDs (Object Storage Daemon). There's no such thing as an option what to choose from ceph, it's completely up to you how you use it. You only have to create the specific pools and users (clients) and tell your applications how to connect to ceph, which pool to use and which client it is. Of course, there's a lot more to be aware of (redundancy, failover scenarios, crush rules etc.) but maybe this is enough to get a grasp of it. I'd recommend to give it a try with ceph, there are several ways to install minimal clusters without much effort.

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answered 2020-06-16 02:08:18 -0600

OpenStack exists, Ceph exists, but there is no such thing as OpenStack Ceph.

I think your questions are answered by this web page: In short, Ceph is Object Storage at its core, but also presents block devices through its RBD interface and a distributed filesystem through CephFS. Both block devices and filesystems are implemented using objects.

However, I don't think files are stored as objects. Filesystems are.

I am not sure if you can install Ceph without RBD and CephFS. Why would you? To learn more about installing Ceph:

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@Bernd is right, ceph is not an openstack component but a standalone software-defined storage solution.

eblock gravatar imageeblock ( 2020-06-16 09:44:31 -0600 )edit

thanks guys - i kept thinking that Ceph is one of the Openstack services but it isn't. Does Ceph work well with Openstack? I am curious why Openstack does not include ceph as one of its services.

happy75 gravatar imagehappy75 ( 2020-06-16 20:37:15 -0600 )edit

Also is Ceph just a "backend" storage? or do you actually need to install cinder or swift with Ceph ? Say for example, if you require block storage, can you just install ceph without installing cinder - would it still work or do you actually need cinder and ceph?

happy75 gravatar imagehappy75 ( 2020-06-16 20:39:12 -0600 )edit

Does Ceph work well with OpenStack? It's the most popular storage backend for Cinder. See and click on Deployment Decisions.

Bernd Bausch gravatar imageBernd Bausch ( 2020-06-17 01:09:07 -0600 )edit

If you want to use Ceph for volumes and/or volume backup, you need Cinder.

If you want it for objects, it replaces Swift and you don't need Swift anymore.

You can also use it as a backend for Nova's ephemeral storage.

Bernd Bausch gravatar imageBernd Bausch ( 2020-06-17 01:13:36 -0600 )edit

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Asked: 2020-06-16 01:34:05 -0600

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Last updated: Jun 16 '20