CERN

Question ________________________________Response__________________________________
Site and Endpoints
What is the site name? CERN
Which endpoint URLs do your archival systems expose? srm://srm-Experiment.cern.ch and root://castorExperiment.cern.ch, where Experiment is one of alice, atlas, cms, lhcb, public. For ALICE, only the root endpoint is available.
How is tape storage selected for a write (choice of endpoint, specification of a spacetoken, namespace prefix). Choice of endpoint and specification of a spacetoken. In some configurations (e.g. for ATLAS), the namespace prefix implies a choice of spacetoken.
Queue
What limits should clients respect?  
---> Max number of outstanding requests in number of files or data volume infinite
---> Max submission rate for recalls or queries Up to about 10 Hz.
---> Min/Max bulk request size (srmBringOnline or equivalent) in files or data volume 1 to 1000. The upper limit is not hard but being SRM based on XML, larger counts make requests handling heavier.
Should clients back off under certain circumstances? YES
---> How is this signalled to client? SRM_INTERNAL_ERROR at request level and SRM_FILE_BUSY at file level returned by SRM. Stalling client by xrootd.
---> For which operations? For SRM, any synchronous operation. For xrootd, any operation can be stalled by the server.
Is it advantageous to group requests by a particular criterion (e.g. tape family, date)? YES absolutely. This helps to avoid requesting same tape over-and-over again in a short period of time.
---> What criterion? Simply grouping as many requests as possible should be enough
Prioritisation
Can you handle priority requests? YES
---> How is this requested? Selected groups of users might have higher priorities than others. However, this is balanced between experiments. Contact Castor.Support@cernNOSPAMPLEASE.ch.
Protocol support
Are there any unsupported or partially supported operations (e.g. pinning) ? Pinning is not supported.
Timeouts
What timeouts do you recommend? At least 1 day to overcome interventions.
Do you have hardcoded or default timeouts? NO
Operations and metrics
Can you provide total sum of data stored by VO in the archive to 100TB accuracy? YES
Can you provide space occupied on tapes by VO (includes deleted data, but not yet reclaimed space) to 100TB accuracy? YES
How do you allocate free tape space to VOs? By a scriot running periodically. Defined number of new tapes (usually 1) is allocated into a tape pool per VO as needed. The check is every 15 minutes.
What is the frequency with which you run repack operations to reclaim space on tapes after data deletion? Once / week on selected tape pools. On experiment tape pools, only major repack campaigns are done automatically. Exception is if experiment perform deletion campaign in which case, we can recover the space sooner.
Recommendations for clients
Recommendation 1  
---> Information required by users to follow advice  
Recommendation 2  
Buffer Management
Should a client stop submitting recalls if the available buffer space reaches a threshold?  
---> How can a client determine the buffer used and free space?  
---> What is the threshold (high water mark)?  
---> When should the client restart submission (low water mark)?  
If the client does not have to back off on a full buffer, and you support pinning, how is the buffer managed?  
---> Is data moved from buffer to another local disk, either by the HSM or by an external agent?  
Additional questions
Should any other questions appear in subsequent iterations of this survey?  

-- OliverKeeble - 2018-01-30 -- OliverKeeble - 2018-01-30

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Topic revision: r2 - 2018-04-19 - OliverKeeble
 
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