dCache Information Providers - Some details

by Ron Trompert

The information providers provide:

GlueSAStateAvailableSpace
GlueSAStateUsedSpace
GlueSAStateAvailableSpace
GlueSAStateUsedSpace
GlueSARetentionPolicy
GlueSAAccessLatency
GlueSATotalOnlineSize
GlueSAUsedOnlineSize
GlueSAFreeOnlineSize
GlueSATotalNearlineSize
GlueSAUsedNearlineSize
GlueSAFreeNearlineSize

The online sizes are obtained by quering dCache for specific pool groups for total and used spaces (at SARA). Sites need to provide this information because the information provider does not know which pool group to query. A storage area in dCache is a pool group. The nearline sizes should be specified by sites if they have tape systems. The GlueSA have names in the form of <vo>:<retention policy>:<access latency>. There can be a many to one mapping with regard to the VOInfo object to the SA. So SA are aggregates spaces.
In the information providers: Total=Free+Used.
Only spaces are published that still have a lifetime of at least one hour, is still valid, have a non NULL space description and a non NULL vogroup assigned to it. This excludes the implicit reservations.
About the new proposal. The work necessary to get this published would be a matter of a few weeks. Multiple ACBRs can be relatively easily be obtained from the dCache srm database. This in order to provide information about shared spaces. The GlueSA class can be easily used to publish the "hidden" space. The VOInfo object (linked the a GlueSA) can be used in order to be enable future releases of dCache to use space tokens for reading or staging data. But as Paul Millar pointed out to me, care must be taken not to break the Glue 1.3 schema. This matter needs some further investigation.

-- FlaviaDonno - 17 Jun 2008