[glue-wg] Updated thoughts...

[Maarten Litmaath]

Paul Millar wrote:

>>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

Yes, in WLCG we want it like that, but I wondered whether it is necessary
to insist there be exactly 1 access latency.

It does seem to make sense with the current ordered set of values:

     Online < Nearline < Offline

But what about an SRM v1 or a Classic SE that has unspecified subsets of
its name space going to tape (current practice): one might want to list
both Online and Nearline as potential guaranteed latencies - some files
have Online, other files have Nearline as their _guaranteed_ latency.
A single value Nearline might suggest that everything goes to tape.

Probably devil's advocate, but in GLUE we should be careful with
insisting that a particular property shall _always_ hold...
Thanks,
	Maarten