[Sheepdog] object sizes

[Christoph Hellwig]

On Sat, Nov 12, 2011 at 12:04:47AM +0800, Liu Yuan wrote:
> I am not sure what is reflink. is it synonym to snapshot? IIC, yes, the
> new storage infrastructure named 'farm' will support clsuter-wide snapshot.

It basically is a file level snapshot, see here for an introduction:

	http://oss.oracle.com/osswiki/OCFS2/DesignDocs/ReflinkOperation

> Simply put, it somewhat resembles git a lot (both code and idea level).
> there are three object type, named 'data, trunk, snapshot' that is
> similar to git's 'blob, tree, commit'.
> 
> 'data' is just sheepdog's data object, only named by its sha1ed content.
> So the data objects with the same content will be mapped to only single
> sha1 name, thus achieve node-wide data sharing.
> 
> 'snapshot' object will serve to support snapshot which contains the
> snapshoted trunk, that is 'directory' of the that-time data objects on
> each node. The trunk object will provide a means to find data objects.
> This will support cluster-wide snapshot.
> 
> The 'farm' doesn't has any constraint to object data size. Hope this helps.

How well do snapshots / COW images work with large objects?

Either way, I'm looking forward to see your work.