Speaker
Description
Impact
As of November 2008, a total of 474 links have achieved commissioning according to the metrics required by the DDT task force, which are currently:
- 20 MB/s averaged over 24 hours for links with source at the CERN Tier 0 or at a Tier 1
- 5 MB/s averaged over 24 hours for links with source at a Tier 2
The 474 commissioned links are divided as follows:
- All of the 56 links between CERN and the 7 T1s supporting the CMS VO are commissioned.
- 272 downlinks from T1s to T2s are commissioned, representing 77% of the total mesh of 352 links between T1s and T2s supporting the CMS VO which have joined the LoadTest infrastructure.
- 41 uplinks from T2s to the respective associated T1s are commissioned, representing 85% of the total. In addition, 88 uplinks between T2s and non-associated T1s are also commissioned.
- 17 T2-T2 cross-links are also commissioned.
The experience gained in link commissioning has been collected to provide a useful knowledge base for the sites in debugging transfer issues.
Keywords
HEP, Data Management
Conclusions and Future Work
A focused effort to debug transfer links within CMS sites proved to be useful in helping to maintain a working
system for data transfers, documenting common problems and solutions, and alerting site administrators to current problems. This effort continued in 2008 with requirements and testing exercises that more closely match the CMS computing model and expected data transfer patterns when data taking will resume in 2009.
URL for further information
https://twiki.cern.ch/twiki/bin/view/CMS/DDT
Detailed analysis
The CMS experiment at CERN is preparing for LHC data taking in several computing preparation activities. In 2007 a traffic load generator infrastructure was designed and deployed to equip the WLCG sites which support the CMS Virtual Organization with a means for debugging, load-testing and commissioning data transfer routes among CMS Computing Centres. The LoadTest is based upon PhEDEx as a reliable, scalable dataset replication system, which fully supports the gLite File Transfer Service as a backend for file replication. The Debugging Data Transfers (DDT) Task Force was created to coordinate the debugging of data transfer links by designing and enforcing a clear procedure to debug problematic links and by assisting the sites in solving technical problems. Links are tested against a set of agreed metrics in an independent debugging environment and moved to a production environment when the commissioning conditions are achieved. Common technical issues are documented for the sites.
