Abstract
The Italian community in CMS has built a geographically distributed network in which all the data stored in the Italian region are available to all the users for their everyday work. This activity involves at different level all the CMS centers: the Tier1 at CNAF, all the four Tier2s (Bari, Rome, Legnaro and Pisa), and few Tier3s (Trieste, Perugia, Torino, Catania, Napoli, ...). The federation uses the new network connections as provided by GARR, our NREN (National Research and Education Network), which provides a minimum of 10 Gbit/s to all the sites via the GARR-X[2] project. The federation is currently based on Xrootd[1] technology, and on a Redirector aimed to seamlessly connect all the sites, giving the logical view of a single entity. A special configuration has been put in place for the Tier1, CNAF, where ad-hoc Xrootd changes have been implemented in order to protect the tape system from excessive stress, by not allowing WAN connections to access tape only files, on a file-by-file basis. In order to improve the overall performance while reading files, both in terms of bandwidth and latency, a hierarchy of xrootd redirectors has been implemented. The solution implemented provides a dedicated Redirector where all the INFN sites are registered, without considering their status (T1, T2, or T3 sites). An interesting use case were able to cover via the federation are disk-less Tier3s. The caching solution allows to operate a local storage with minimal human intervention: transfers are automatically done on a single file basis, and the cache is maintained operational by automatic removal of old files.
Highlights
Participates to the CMS Collaboration with a large number of physicists, distributed in 16 Institutions, and coordinated by INFN
Data custodiality and central processing activities are mostly performed at the Tier1 at CNAF (Bologna), while analysis activities are carried out at the four Tier2 sites (Pisa, Bari, Rome, Legnaro/Padova)
The only way to access those file is via a direct stage-in command issued before the Xrootd attempt is tried. Since this can be a limiting factor in the case when we want to be able to trigger automatic recall, a second mechanism has been put in place: direct requests to the CNAF Xrootd servers are allowed for tape-only files, but are not triggering direct recalls; these are instead queued in the GEMSS system, which makes sure that recalls are done safely for the tape drives, and for example joining requests for files on the same tape
Summary
This content has been downloaded from IOPscience. Please scroll down to see the full text. Ser. 513 042013 (http://iopscience.iop.org/1742-6596/513/4/042013) View the table of contents for this issue, or go to the journal homepage for more. Download details: IP Address: 140.105.48.10 This content was downloaded on 10/08/2016 at 14:52 Please note that terms and conditions apply. 20th International Conference on Computing in High Energy and Nuclear Physics (CHEP2013) IOP Publishing. Journal of Physics: Conference Series 513 (2014) 042013 doi:10.1088/1742-6596/513/4/042013. T.Boccali, G.Donvito, D.Diacono, G.Marzulli, A.Pompili, G.Della Ricca, E.Mazzoni, S.Argiro, D.Gregori, C.Grandi, D.Bonacorsi, L.Lista, F.Fabozzi, L.M.Barone, A.Santocchia, H.
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