[glue-wg] New attribute for GLUE 2.1: StorageShare.ViewID

[Paul Millar]

Hi all,

After playing some more with GLUE 2.0 (and getting feedback from someone 
trying to use it!), there seems to be a missing concept in StorageShare, 
which I'll call "views".

The idea is to allow publishing two (or more) groups of Storage Shares 
such that, within such a group, the Storage Shares can be 
non-overlapping but shares from different groups can overlap.

Each group of non-overlapping shares provides a different "view" on the 
storage system.  It's likely that the underlying hardware is the same 
(with the sum of StorageShareCapacity.Total giving the same value), but 
the different views (different groups of storage shares) would partition 
this storage differently.

Here's a more concrete example: consider a storage service that allows 
capacity to be reserved but doesn't bind those reservations to 
particular hardware.  This is difficult to publish currently; but, these 
could be published as two different views: one view shows the hardware, 
the other shows the reservations.

I believe we can add views while remaining backwards compatible with 
GLUE 2.0 attributes and semantics; in particular, we can keep the 
semantics of SharingID unmodified for existing publishers.

Here's the proposal:

     Attribute: ViewID

     Type: LocalID_t

     Mult: 0..1 ("optional")

     Unit: <none>

     Description:

     A local identifier that groups together similar Storage
     Shares.  Two shares are part of the same view if and only if
     both do not publish a ViewID or both publish the same
     ViewID value.  Two Storage Shares that are part of the
     same view and have either distinct SharingID values or
     the same "dedicated" SharingID value are non-overlapping,
     otherwise they may overlap.

Since the attribute is optional, existing publishers will continue to 
work, but will refrain from publishing a ViewID attribute.  Since not 
publishing ViewID places the Storage Share objects in the same view, the 
GLUE 2.0 SharingID semantics is preserved.

Cheers,

Paul.