LHCb Computing Resources: 2019 requests and reassessment of 2018 requests

LHCb Computing Resources: 2019 requests and reassessment of 2018 requests LHCb-PUB-2017-019 09/09/2017 LHCb Public Note Issue: 0 Revision: 0 Reference: LHCb-PUB-2017-019 Created: 30 th August 2017 Last modified: 5 th September 2017 Prepared By: LHCb Computing Project C. Bozzi/Editor

Introduction Last modified: 5th September 2017 Abstract This document presents the computing resources needed by LHCb in 2019 and a reassessment of the 2018 requests, as resulting from the current experience of Run2 data taking and minor changes in the LHCb computing model parameters. page iii

Introduction Last modified: 5th September 2017 Table of Contents 1. INTRODUCTION... 1 2. THE LHCB COMPUTING MODEL AND PROCESSING PLANS... 1 3. EXTRAPOLATION OF STORAGE RESOURCES AT THE END OF 2017... 2 4. RESOURCES NEEDED IN 2018 AND 2019... 6 5. SUMMARY OF REQUESTS... 7 iv page iv

Introduction Last modified: 5th September 2017 List of Tables Table 2-1: Assumed LHC proton-proton and heavy ion running time in 2018.... 2 Table 4-1: Estimated CPU work needed for the different activities (unchanged)... 6 Table 4-2: Disk Storage needed for the different categories of LHCb data.... 6 Table 4-3: Tape Storage needed for the different categories of LHCb data.... 7 Table 5-1: CPU power requested at the different Tier levels.... 7 Table 5-2: LHCb Disk request for each Tier level. For countries hosting a Tier1, the Tier2 contribution could also be provided at the Tier1.... 8 Table 5-3: LHCb Tape request for each Tier level.... 8 List of Figures Figure 1: (blue) 2016 disk requests, disk occupancies on (red) April 1 st 2017 and (green) September 1 st 2017, for different storage classes. The 2016 pledge is shown in violet.3 Figure 2: (blue) 2016 tape requests, tape occupancies on (red) April 1 st 2017 and (green) September 1 st 2017, for different storage classes. The 2016 pledge is shown in violet.3 Figure 3: (top) increment of and (bottom) required disk space at the end of the 2017 WLCG year, following the three extrapolations criteria described in the text. The violet histogram in the Total column represents the 2017 disk pledge.... 4 Figure 4: (top) increment of and (bottom) required tape space at the end of the 2017 WLCG year, following the three extrapolations criteria described in the text. The violet histogram in the Total column represents the 2017 tape pledge.... 5 page v

Introduction Last modified: 5th September 2017 1. Introduction This document presents the computing resources needed by LHCb in the 2019 WLCG year 1 and a reassessment of the 2018 requests. This document is based on the latest measurements of the LHCb computing model parameters and latest updates of the LHC running plans. In particular, the LHC efficiency in the first months of 2017 was worse than the one used to estimate the requests in previous reports. The impact of this change on 2018 and 2019 requests is assessed. The LHCb computing model, its implementation, recent changes and processing plans are described in Section 2. The determination of the storage resources needed at the end of 2017 is given in Section 3, where the LHC performance in the first part of 2017 is extrapolated until the end of the 2017 data taking. Resource estimates in 2018 and 2019 are given in Section 4. A summary of the requests is given in Section 5. 2. The LHCb Computing Model and processing plans A detailed description of the LHCb Computing Model is given elsewhere [LHCb-PUB-2012-014 and LHCb-PUB-2011-009]. Subsequent reports [LHCb-PUB-2013-002, LHCb-PUB-2013-014, LHCb-PUB- 2014-014, LHCb-PUB-2015-003, LHCb-PUB-2016-003, LHCb-PUB-2016-022, LHCb-PUB-2017-009] discussed further changes and their impact on the required resources. The most relevant features of the LHCb Computing Model are reported below. Data are received from the online system in several streams, o o A FULL stream, where RAW events are reconstructed offline, then filtered (stripping) according to selection criteria specific for given analyses (stripping lines). A TURBO stream, in which the output of the online reconstruction is stored, turned offline into a micro-dst format and made available to analysts RAW data of all streams are saved on tape at Tier0 and at one selected Tier1. The output of the offline reconstruction (RDST) of the FULL stream are saved on tape, the stripping output is replicated and distributed on disk storage. The stripping output can be in either DST format that contains the complete reconstructed event, or micro-dst format, where only signal candidates and possible additional information is included. Stripping lines are designed such, that as many lines as possible are written in micro-dst. The micro-dst files from the TURBO stream are replicated on disk storage. All datasets made available for analysis on disk are also archived on tape for data preservation. The production of simulated events runs continuously, with the aim of producing signal and background samples for a total number of simulated (and reconstructed) events which is of the order of 15% of the total number of collected real data events. Estimates of the resources required for 2018 and 2019 are re-computed by taking into account the following changes with respect to LHCb-2017-022: 1 For the purpose of this document a given year always refers to the period between April 1 st of that year and March 31 st of the following year. page 1

Extrapolation of storage resources at the end of 2017 Last modified: 5th September 2017 The LHC efficiency for physics observed in the first part of the 2017 data taking is significantly lower than expected (40% instead of 60%); the extrapolations of the storage resources needed at the end of the 2017 WLCG year (Section 3) are therefore lower than previous estimates. This enables LHCb to use the available disk space in 2017 by relaxing two measures that had impact on physics analysis but nevertheless had to be taken to cope with the anticipated shortage of disk space: o The fraction of TURBO data (35%) parked on tape during the 2016 data taking will be replicated on disk. TURBO data is not being parked on tape during the 2017 data taking. There will be no parking foreseen in 2018 either. o A full stripping cycle will be performed on 2016 data in 2017. The MDST.DST files that were saved on tape as a backup of all events written to micro-dst format are no longer saved, since the content of the micro-dst files is now well established. This reduces the tape requests by 6PB. This master DST was introduced to enable fast regeneration of micro-dst files in cases there would be missing information, during the validation phase of the analyses on Run2 datasets. It is no longer needed. Additional resources for analysis preservation activities have been made, amounting to 7kHS06 CPU power and 0.1 PB disk space at the Tier0. Assumptions that are unchanged with respect to LHCb-2017-022 include: Running time for proton collisions of 7.8 million seconds in 2018, corresponding to an efficiency for physics of about 60% (Table 2-1); A month of heavy ion collisions in 2018, with concurrent heavy ion proton collision in fixed target configuration, will also take place (Table 2-1). 2017 data will be fully re-stripped in 2017 and incrementally stripped in 2018. a legacy re-stripping of all Run 2 data will take place during LS2 in 2019 Two copies of the most recent processing pass on both data and simulation are kept on disk. For the next-to-most recent data processing pass the number of copies are two for data, one for simulation. Throughput of the stripping of 195MB per live second of the LHC in 2018. Throughput of TURBO of 118MB per live second of the LHC in 2018. FULL stream trigger rate of 9.4kHz in 2018. Parameter 2018 Proton physics LHC run days 150 LHC efficiency 0.60 Approx. running seconds 7.8 10 6 Number of bunches 2448 Heavy Ion physics Approx. running seconds 1.4 10 6 Table 2-1: Assumed LHC proton-proton and heavy ion running time in 2018. 3. Extrapolation of storage resources at the end of 2017 The LHC efficiency observed so far in 2017 is lower than previously foreseen. Therefore, an extrapolation has been made to compute the storage resources that are going to be used by the end of the 2017 WLCG 2 page 2

Extrapolation of storage resources at the end of 2017 Last modified: 5th September 2017 year, by taking the storage occupancy at the end of the 2016 WLCG year as starting point and measuring the occupancy on September 1 st 2017, and by taking into account the other changes mentioned in Section 2. The requests presented in 2016 and the actual storage usage on April 1 st and September 1 st 2017 are shown in Figure 1 (Figure 2) for disk (tape), as well as the 2017 pledges. 30 25 20 15 10 05 Disk requests vs occupancy (PB) 00 Data MC User Buffers Other Total 2016 req April 2017 Sept 2017 2016 pledge Figure 1: (blue) 2016 disk requests, disk occupancies on (red) April 1 st 2017 and (green) September 1 st 2017, for different storage classes. The 2016 pledge is shown in violet. 60 50 40 30 20 10 Tape requests vs occupancy (PB) 00 RAW RDST Archive Total 2016 req April 2017 Sept 2017 2016 pledge Figure 2: (blue) 2016 tape requests, tape occupancies on (red) April 1 st 2017 and (green) September 1 st 2017, for different storage classes. The 2016 pledge is shown in violet. The extrapolation of storage resources to the end of the 2017 WLCG year depends on the LHC performance from the time of this writing until the end of the 2017 data taking. Three scenarios have been considered, where the LHC performs either at the same level observed until now (pessimistic scenario, 40% efficiency), or 50% better (baseline scenario, 60% efficiency), or 100% better (optimistic scenario, 80% efficiency). page 3

Extrapolation of storage resources at the end of 2017 Last modified: 5th September 2017 In addition, based on current experience, it is assumed that simulation continues to accumulate 0.125PB of data per month on disk, and half of that on tape. This is significantly smaller than expected, due to the increased usage of filters (based on the stripping of real data) that allow to save on storage only a fraction of events that pass analysis-specific criteria. Since the MDST.DST files are no longer produced, the tape space that was previously foreseen for MDST.DST (6.8PB) is now set to the tape space (0.7PB) currently taken by MDST.DST. Moreover, 2PB of disk space were recovered by following dataset popularity studies. The expected increments and total amounts of disk (tape) in these three scenarios are shown in Figure 3 (Figure 4). By taking as baseline the scenario where the LHC run at 60% efficiency in the remaining months of 2017, the disk (tape) increment will be 7.1PB (13.7PB) which, taking into account the current storage usage, leads to an expected total disk (tape) usage of 29.6PB (54.2PB), i.e. 15% (20%) less than the 2017 pledges. Disk increments Apr17-Apr18 (PB) 9 8 7 6 5 4 3 2 1 0 Data MC User Buffers Other Total Pessimistic Baseline Optimistic Disk Apr18 extrapolations (PB) 40 35 30 25 20 15 10 05 00 Data MC User Buffers Other Total Pessimistic Baseline Optimistic Pledge Figure 3: (top) increment of and (bottom) required disk space at the end of the 2017 WLCG year, following the three extrapolations criteria described in the text. The violet histogram in the Total column represents the 2017 disk pledge. 4 page 4

Extrapolation of storage resources at the end of 2017 Last modified: 5th September 2017 Tape increments Apr17-Apr18 (PB) 18 16 14 12 10 8 6 4 2 0 RAW RDST Archive Total Pessimistic Baseline Optimistic Tape Apr18 extrapolations (PB) 80 70 60 50 40 30 20 10 0 RAW RDST Archive Total Pessimistic Baseline Optimistic 2017 pledge Figure 4: (top) increment of and (bottom) required tape space at the end of the 2017 WLCG year, following the three extrapolations criteria described in the text. The violet histogram in the Total column represents the 2017 tape pledge. page 5

Resources needed in 2018 and 2019 Last modified: 5th September 2017 4. Resources needed in 2018 and 2019 Table 4-1 presents, for the different activities, the CPU work estimates when applying the model defined above. The only change with respect to the previous requests shown in LHCb-PUB-2017-009 is due to the resources added for analysis preservation (7kHS06, a 1.4% effect). CPU Work in WLCG year (khs06.years) 2018 2019 Prompt Reconstruction 49 0 First pass Stripping 20 0 Full restripping 0 61 Incremental (re-)stripping 10 15 Processing of heavy ion collisions 38 0 Simulation 342 411 VoBoxes and other services 4 4 User Analysis 32 38 Analysis preservation 7 7 Total Work (khs06.years) 502 536 Table 4-1: Estimated CPU work needed for the different activities (unchanged) Table 4-2 presents, for the different data classes, the forecast total disk space usage at the end of the years 2018 and 2019 when applying the baseline model described in the previous section. Table 4-3 shows, for the different data classes, the forecast total tape usage at the end of the years 2018 and 2019. The disk space in 2018 is 0.7PB (1.6%) lower than the previous requests shown in LHCb-PUB-2017-009, with small rearrangements between the stripping, TURBO and simulated data. The tape space in 2018 is 18.7PB (19%) lower, due to the suppression of MDST.DST (6.1PB less space than foreseen) and to the smaller space needed by RAW, RDST and ARCHIVE (4.9PB less), as a direct consequence of the lower LHC efficiency in 2017. For 2019, the disk space is 1.8PB (3.5%) lower than the previous requests shown in LHCb-PUB-2017-009, while tape requests are 19.2PB (18%) lower. Disk storage usage forecast (PB) 2018 2019 Stripped real data 18.2 23.0 TURBO Data 4.2 4.2 Simulated Data 11.3 13.7 User Data 1.8 1.9 Heavy Ion Data 4.2 4.2 RAW and other buffers 1.2 1.2 Other 0.6 0.6 Analysis preservation 0.1 0.1 Total 41.6 48.9 Table 4-2: Disk Storage needed for the different categories of LHCb data. 6 page 6

Summary of requests Last modified: 5th September 2017 Tape storage usage forecast (PB) 2018 2019 Raw Data 40.8 40.8 RDST 14.8 14.8 MDST.DST 0.7 0.7 Heavy Ion Data 3.7 3.7 Archive 19.2 25.9 Total 79.2 85.9 Table 4-3: Tape Storage needed for the different categories of LHCb data. 5. Summary of requests Table 5-1 shows the CPU requests at the various tiers, as well as for the HLT farm and Yandex. We assume that the HLT and Yandex farms will provide the same level of computing power as in the past, therefore we subtract the contributions from these two sites from our requests to WLCG. The required resources are apportioned between the different Tiers taking into account the capacities that are already installed. The disk and tape estimates shown in previous section have to be broken down into fractions to be provided by the different Tiers using the distribution policies described in LHCb-PUB-2013-002. The results of this sharing are shown in Table 5-2 and Table 5-3. It should be noted that, although the total storage capacity is given globally for the 8 Tier1 sites pledging resources to LHCb, it is mandatory that the sharing of this storage between Tier1 sites remains very similar from one year to another: the annual increments are small, existing data is expected to remain there, runs assigned to each Tier1 are also expected to be reprocessed there and the analysis data is stored at these same Tier1s. There is a level of flexibility offered when replicating the data to a second Tier1 that takes into account the available space. However, a baseline increase is mandatory at all sites, otherwise they can no longer be used for the placement of new data. LHCb will be upgraded during the LHC shutdown of 2019-2020, and will resume data taking in 2021. There will be many changes in the computing activities in the upgrade era, that will need to be prepared and properly tested before 2021. These activities are being planned in a Technical Design Report of software and computing for the LHCb upgrade, due by the end of 2017. The part more related to the computing model and the required computing resources will be finalized in a document to be released in mid 2018. The computing resources required in 2020 will depend on the outcome of the upgrade activities and on the detailed planning, which is not ready yet. Therefore, the LHCb computing requests for 2020 have not been presented in this report. CPU Power (khs06) 2018 2019 Tier 0 88 93 Tier 1 253 271 Tier 2 141 152 Total WLCG 482 516 HLT farm 10 10 Yandex 10 10 Total non-wlcg 20 20 Grand total 502 536 Table 5-1: CPU power requested at the different Tier levels. page 7

Summary of requests Last modified: 5th September 2017 Disk (PB) 2018 2019 Tier0 11.4 14.2 Tier1 24.5 27.9 Tier2 5.7 6.8 Total 41.6 48.9 Table 5-2: LHCb Disk request for each Tier level. For countries hosting a Tier1, the Tier2 contribution could also be provided at the Tier1. Tape (PB) 2018 2019 Tier0 33.6 35.0 Tier1 45.6 50.9 Total 79.2 85.9 Table 5-3: LHCb Tape request for each Tier level. 8 page 8