The LHCb Italian Tier-2 Domenico Galli, Bologna INFN CSN1 Roma,
The LHCb Italian Tier-2. 2 Domenico Galli Aim of LHCb Tier-2s In the LHCb Computing Model Tier-2s are used (at least in countries also provided with a Tier-1) as a pure centrally scheduled Monte Carlo simulation facility. In the LHCb Computing Model Analysis is not performed on Tier-2s. A LHCb Tier-2 consists in a PC-farm with a small disk buffer (3 TB in steady state) used as a temporary cache until data transfer to Tier-1. LHCb-Italy proposes to build 1 Tier-2 hosted at Bologna-CNAF, together with Italian Tier1.
The LHCb Italian Tier-2. 3 Domenico Galli Why LHCb Analysis at Tier-1? LHCb analysis jobs consist in selecting the events (stripped DST) stored at Tier-1 to focus on one particular analysis channel: Typical analysis jobs run on a ~10 6 event sample. Some analysis jobs will run on a larger ~10 7 event sample. Average event reduction of a factor of 5. Analysis input is completely stored at each Tier-1. Analysis output ( GB) can be processed by a small Tier-3 facility. Physics Analysis Local Analysis Paper Selected DST+RAW 119 TB Event Tag Collection 20 TB Available at each Tier-1 n-tuple / User DST + User TAG Typical: 20 GB Large: 200 GB
The LHCb Italian Tier-2. 4 Domenico Galli Comparison between 2 models: Analysis job at Tier-2: Analysis job at Tier-1: Data accessed at Tier-1 per analysis job are the same. But the second is faster and less expensive in terms of hardware, infrastructure, staff resources and WAN load. Why LHCb Analysis at Tier-1? (II) Tier-1 DST+RAW+TAG 139 TB Output GB 139 TB Tier-1 Tier-2 DST+RAW+TAG 139 TB Buffer Output GB 139 TB WAN LAN
The LHCb Italian Tier-2. 5 Domenico Galli Why Tier-2 at CNAF? This model would allow maximum flexibility in moving resources back/forth between Tier-2 and Tier-1 to optimize resource exploitation. (to satisfy peak MC/analysis request). Simply by means of a software operation. No competition among Italian sites on Tier-2 resources, since MC production is centrally scheduled. Italian LHCb people involved in computing are mainly located in Bologna.
The LHCb Italian Tier-2. 6 Domenico Galli Tier-2 at CNAF Given the growing profile, LHCb Tier-2 is at maximum a +10% perturbation of CNAF Tier-1 resources. Same building. Same cooling system. Same fire alarm and surveillance. Same network. Same electric power and UPS. Etc. Same trained and skilled management and technical staff. LHCb experiment staff from Bologna Already heavily involved in LHCb computing; Established strict collaboration with the CNAF staff.
The LHCb Italian Tier-2. 7 Domenico Galli LHCb Tier-2 Exploitation in the Next Years From now on, practically speaking, an almost continuous MC production is foreseen for LHCb. Mainly for: Physics studies; HLT studies. Order of 100's Mevents/year.
The LHCb Italian Tier-2. 8 Domenico Galli LHCb Tier-2 Size and Cost We are sizing the Italian Tier-2 to be 15% of the total Tier-2 resources of the whole LHCb collaboration. 15% = Italian fraction of CORE funds; 15% = fraction of Italian physicists with respect of the total involved in the LHCb experiment.
The LHCb Italian Tier-2. 9 Domenico Galli LHCb Tier-2 Additional Size and Cost (according to LHCb Computing Model) Strictly according to current LHCb Computing Model total CPU [€/Si2k] Disk [€/GiB] CPU running [MSi2k] CPU Box running Disk running [TiB] CPU replacement [MSi2k] 0.34 Disk replacement [TiB] 1 CPU to be acquired [MSi2k] Disk to be acquired [TiB] CPU cost [k€] Disk cost [k€] Total cost [k€]
The LHCb Italian Tier Domenico Galli LHCb Tier-2 Additional Infrastructures CPU [MSi2K] Disk [TiB]12333 Electric Power [kW] N. PC Box N. Racks35664 Power+cooling [kW] kSi2k → 110 W 1 TiB → 70 W
The LHCb Italian Tier Domenico Galli LHCb Requests for k€: Tier-2 resources (95 dual-processor box + 1 TiB Disk). Since resources are allocated at CNAF, resource management could be flexible: CPUs can be moved from Tier-1 queues to Tier-2 queues and back with software operations. But Tier-2 have to be logically separated by Tier-1 (e.g.: different batch queues).