Hi Stephen,
yes, replacing "files" with "data object" in the text it is fine, but, in my opinion, we should also perform the following changes:

* Add to StorageEndpoint element the following attribute:

SupportedObjects

CloudStorageT_t

Supported data object formats (ex. Image disks, files, generic objects, etc…)

. For the use is important to know which kind of storage the service provides, if it is storage for files, disk images, EBS attached storage, etc...
* Add to StorageShare the following attributes:

MaxObjectSize	UInt64	0..1	MB	Maximum size of a data object who can be stored in this share
MinObjectSize	UInt64	0..1	MB	Minimum size of a data object who can be stored in this share

This is very important for the user (especially for EBS storage, where the storage object is a disk attached to a VM) to choose which storage service is better for their need and for the authomatic systems to perform auto-scaling of the storage.

Of course, we could use the extensions to add these attributes and do not change the standard...

Regarding the capabilities for the storage taken from CDMI or other cloud standards (ex. support for file encryption, single file ACLs, etc...), they may go into the Capability attribute of the StorageEndpoint, which is an open enumeration, so we need to add nothing for that.

Cheers,
Salvatore.

On 05/11/2013 11:59, stephen.burke@stfc.ac.uk wrote:

Behalf Of Salvatore Pinto said: That is true, Storage schema is very close to the Grid version and can be indeed rewritten inheriting the Storage elements or just modifyi-ing them. From my point of view, the big difference between Cloud and Grid storage is that Cloud storage is not file-oriented like the grid one but more object oriented (where an object can be a file, a disk image, a stream or a generic object). So, in this view, the "Grid" storage is a specialization of the "Cloud" one (where object type=files) and it would be probably better to change the GLUE 2.0 Storage element to consider objects instead of files and have one single entity. What do you think of that?

I don't think the current schema really represents files - the word "file" may appear in the text but you could replace it with "data object" without changing anything. It isn't feasible to publish information about individual files, all we have is summary information about larger blocks of storage. Also storage systems presumably don't have the biggest difference between cloud and grid computing services, namely that they aren't persistent and can be created and destroyed - storage has to be persistent to be useful!

CDMI metadata are mostly related to file-level options, for example ACLs, file redundancy, file encryption, etc... (source: http://cdmi.sniacloud.com/cdmi_spec/16-metadata/16-metadata.htm). We could try to extend these attributes at system level and assign them to the storage service or other entities, but with this we would break one of the main features of the Cloud storage, which is the freedom for the user to ecrypt one file and not another, share one with the world, one with only his colleagues and another restricted.

You certainly wouldn't want to publish the state of individual files, but you may want to advertise the capability to do various things, similarly to the support for different access protocols. Stephen