On Friday 11 April 2008 03:34:55 Maarten.Litmaath@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.