[glue-wg] Updated thoughts...

[Paul Millar]

On Friday 11 April 2008 03:34:55 Maarten.Litmaath at cern.ch wrote:
> On Wed, 9 Apr 2008, Paul Millar wrote:
> > 	b. some places have operation practise that they "just add more tapes"
> > when the space looks like its filling up,
>
> In that case it may still be interesting to publish the current total.

Sure, that's an option that GLUE should support; but equally, a grid might 
choose not ... it's a policy decision.  This information should be optional.

I'm more concerned with problem a. (can't reliably get that information).

[StorageEnvironment RP multiplicity]
> I argued that GLUE probably should allow for the RP being multi-valued,
> and probably the AccessLatency as well.  In WLCG/EGEE we would have a
> single value for each normally, so that the Storage Class is clear.

I'm not sure what AccessLatency as a multivalue means: I'd push this attribute 
down to the hardware layer (StorageDatastore/StorageMedia/StorageStorage)

It's possible that we've been talking slightly at cross-purposes.  It seems to 
me that what WLCG means by "access latency" is really the minimum (ie, 
fastest) guaranteed access latency (MGAL):
	D0T1 this is nearline
	D1T0 this is online
	D1T1 this is online

AccessLatency is a property of the hardware, MGAL is a property of the 
StorageEnvironment.  For example, a file, stored in D0T1, may (usually only a 
short period) be available with online latency, when it's available from the 
online Datastore (the cache).

There's a similar distinction between what custodial means at the 
StorageEnvironment (or StorageShare) level compared to at the hardware level 
(Datastore, or whatever).  I guess this is: an StorageEnvironment is 
considered custodial if files are always stored within at least one 
StorageMedia/Datastore that is considered custodial.  So, WLCG is really a 
boolean attribute canStoreAsCustodial (or similar).

I don't know if this helps clarify the multi-RP / multi-AP issue.

[...]
> > I'm not sure having multiple ExpirationMode makes sense.  If, for some
> > reason, two ExpirationModes need to be indicated, could this be done with
> > two different StorageEnvironments?
>
> No.  I argued that in SRM v2.2 the ExpirationMode (a.k.a. Type) does not
> behave like RP and AL: a space that is defined by RP and AL may support
> multiple ExpirationModes.  In a particular space a file may have a finite
> or an infinite lifetime; the SRM may support either or both.  So, at least
> ExpirationMode we would want to be multi-valued within the Environment.

OK, I think I understand.

> > If a StorageEnvironment is advertised as having a RetentionPolicy 
> > Custodial (only) and has two StorageCapacity (a nearline one and an
> > online one), would that be OK?
>
> In WLCG it would seem natural to identify an Environment with a Storage
> Class, in which case the RP and AL need to be treated together.

So, yes.  That would be OK.



> > > [proposal for Storage Components made by Flavia],
> > I'm not sure ... I don't think I've seen it.  Do you a copy somewhere?
> https://forge.gridforum.org/sf/go/doc14619?nav=1

Ta.

Paul.