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Subsection QuestionSorted ascending Response
Protocol support Are there any unsupported or partially supported operations (e.g. pinning) ? All features that dCache and xrootd support natively should work for GridKa, too.
Prioritisation Can you handle priority requests? No.
Operations and metrics Can you provide space occupied on tapes by VO (includes deleted data, but not yet reclaimed space) to 100TB accuracy? Yes
Operations and metrics Can you provide total sum of data stored by VO in the archive to 100TB accuracy? Yes
Timeouts Do you have hardcoded or default timeouts? Yes, we have default timeouts with dCache for flushing and staging of at least 24 hours (may be larger on request). No timeouts are enforced with xrootd.
Operations and metrics How do you allocate free tape space to VOs? We do not allocate space on tape for any VO.
Site and Endpoints How is tape storage selected for a write (choice of endpoint, specification of a spacetoken, namespace prefix). dCache and xrootd both archive into the same tape storage backend.
Queuing Is it advantageous to group requests by a particular criterion (e.g. tape family, date)? In theory, yes, that would be advantageous. But we cannot guarantee that it will stay in that order or grouping. There is only a loose chronological order.
Recommendations for clients    
Queuing → For which operations? srm-bring-online / open
Prioritisation → How is this requested?  
Queuing → How is this signalled to client? srm-bring-online and accessing a file will fail.
Queuing → Max number of outstanding requests  
Queuing → Min/Max bulk request size?  
Queuing → Min/Max requests submitted at one time dCache assignes flush and stage tasks to pools, which all have an upper limit for concurrent active tasks, usually 2k. Requests beyond that are queued. For xrootd the limit is a total of 3200 concurrent flushing and staging tasks.
Queuing → What criterion? Timestamps would be most useful, since tape families don't necessarily match what the VOs use as classification.
Queuing Should clients back off under certain circumstances? SRM feature with dCache: A limit can be set for every request type, including srm-bring-online (10k by default). Once more requests are accumulated, SRM will block and return "overloaded" error. For xrootd, there is no such feature that would reckognise an overload situation. If a file cannot be staged from tape, xrootd will fail on each subsequent request immediately.
Operations and metrics What is the frequency with which you run repack operations to reclaim space on tapes after data deletion? We have defined a threshold for "tape occupancy", which will trigger reclamation per tape.
Site and Endpoints What is the site name? FZK_LCG2
Queuing What limits should clients respect?  
Timeouts What timeouts do you recommend?  
Site and Endpoints Which endpoint URLs do your archival systems expose? srm:{atlassrm-fzk,cmssrm-kit,lhcbsrm-kit}


OliverKeeble - 2018-01-30
Created article.
XavierMol - 2018-04-16
Inserted answers for KIT/GridKa on behalve of Doris Ressmann.
XavierMol - 2018-04-16
Changed format of the tabel
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Topic revision: r2 - 2018-04-16 - XavierMol
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