CTA Publications
2021
CERN Tape Archive: a distributed, reliable and scalable scheduling system
Eric Cano, Vladímir Bahyl, Cédric Caffy, Germán Cancio, Michael Davis, Oliver Keeble, Viktor Kotlyar, Julien Leduc and Steven Murray.
25th International Conference on Computing in High Energy and Nuclear Physics (CHEP 2021).
Published in EPJ Web of Conferences, volume 251:02037 (2021).
The CERN Tape Archive (CTA) provides a tape backend to disk systems and, in conjunction with EOS, is managing the data of the LHC experiments at CERN. Magnetic tape storage offers the lowest cost per unit volume today, followed by hard disks and flash. In addition, current tape drives deliver a solid bandwidth (typically 360 MB/s per device), but at the cost of high latencies, both for mounting a tape in the drive and for positioning when accessing non-adjacent files. As a consequence, the transfer scheduler should queue transfer requests before the volume warranting a tape mount is reached. In spite of these transfer latencies, user-interactive operations should have a low latency. The scheduling system for CTA was built from the experience gained with CASTOR. Its implementation ensures reliability and predictable performance, while simplifying development and deployment. As CTA is expected to be used for a long time, lock-in to vendors or technologies was minimized. Finally, quality assurance systems were put in place to validate reliability and performance while allowing fast and safe development turnaround.
2020
CERN Tape Archive: production status, migration from CASTOR and new features
Eric Cano, Vladímir Bahyl, Cédric Caffy, Germán Cancio, Michael C. Davis, Viktor Kotlyar, Julien Leduc, Tao Lin and Steven Murray.
23rd International Conference on Computing in High Energy and Nuclear Physics (CHEP 2018), Sofia, Bulgaria.
Published in EPJ Web of Conferences, volume 245:04013 (2020).
During 2019 and 2020, the CERN tape archive (CTA) will receive new data from LHC experiments and import existing data from CASTOR, which will be phased out for LHC experiments before Run 3. This contribution will present the statuses of CTA as a service and of its integration with EOS and FTS and the data flow chains of LHC experiments. The latest enhancements and additions to the software as well as the development outlook will be presented. With the development of the repack function, a necessary behind-the-scenes feature, CTA can now take over custodial data and handle media migration, compaction and failures. Further metadata handling optimisations allowed doubling the maximum file rate performance to 200Hz per queue. New retrieve scheduling options are being developed at the request of experiments, with optional FIFO behaviour to ensure better control of the timing for datasets retrieve, and fair share support for competing activities within the same VO. Support for multiple backend databases (Oracle, PostgreSQL, MySQL) have been developed at CERN and contributed by external institutes. This contribution will also report on the challenges of and solutions for migrating data from the decades old CASTOR to CTA. The practical example of the preparation for the migration of ATLAS data will be presented.
2019
CERN Tape Archive (CTA)—from Development to Production Deployment
Michael C. Davis, Vladímir Bahyl, Germán Cancio, Eric Cano, Julien Leduc, and Steven Murray.
23rd International Conference on Computing in High Energy and Nuclear Physics (CHEP 2018), Sofia, Bulgaria.
Published in EPJ Web of Conferences, volume 214:04015 (2019).
The first production version of the CERN Tape Archive (CTA) software is planned to be released during 2019. CTA is designed to replace CASTOR as the CERN tape archive solution, to face the scalability and performance challenges arriving with LHC un–3. In this paper, we describe the main commonalities and differences between CTA and CASTOR. We outline the functional enhancements and integration steps required to add the CTA tape back-end to an EOS disk storage system. We present and discuss the different deployment and migration scenarios for replacing the five CASTOR instances at CERN, including a description of how the File Transfer Service (FTS) will interface with EOS and CTA.
2017
An Efficient, Modular and Simple Tape Archiving Solution for LHC Run–3
S. Murray, V. Bahyl, G. Cancio, E. Cano, V. Kotlyar, D.F. Kruse and J. Leduc.
22nd International Conference on Computing in High Energy and Nuclear Physics (CHEP 2016), San Francisco, USA.
Published in Journal of Physics: Conference Series, volume 898:062013 (2017).
The IT Storage group at CERN develops the software responsible for archiving to tape the custodial copy of the physics data generated by the LHC experiments. Physics Run–3 will start in 2021 and will introduce two major challenges for which the tape archive software must be evolved. Firstly the software will need to make more efficient use of tape drives in order to sustain the predicted data rate of 150 petabytes per year as opposed to the current 50 petabytes per year. Secondly the software will need to be seamlessly integrated with EOS, which has become the de facto disk storage system provided by the IT Storage group for physics data. The tape storage software for LHC physics Run‐3 is code named CTA (the CERN Tape Archive). This paper describes how CTA will introduce a pre-emptive drive scheduler to use tape drives more efficiently, will encapsulate all tape software into a single module that will sit behind one or more EOS systems and will be simpler by dropping support for obsolete backwards compatibility.
2015
Experiences and challenges running CERN's high capacity tape archive
Germán Cancio, Vladimír Bahyl, Daniele Francesco Kruse, Julien Leduc, Eric Cano and Steven Murray.
21st International Conference on Computing in High Energy and Nuclear Physics (CHEP 2015), Okinawa, Japan.
Published in Journal of Physics: Conference Series, volume 664(4):042006 (2015)
CERN's tape-based archive system has collected over 70 Petabytes of data during the first run of the LHC. The Long Shutdown is being used for migrating the complete 100 Petabytes data archive to higher-density tape media. During LHC Run--2, the archive will have to cope with yearly growth rates of up to 40--50 Petabytes. In this contribution, we describe the scalable setup for coping with the storage and long-term archival of such massive data amounts. We also review the challenges resulting and mechanisms devised for measuring and enhancing availability and reliability, as well as ensuring the long-term integrity and bit-level preservation of the complete data repository. The procedures and tools for the proactive and efficient operation of the tape infrastructure are described, including the features developed for automated problem detection, identification and notification. Finally, we present an outlook in terms of future capacity requirements growth and how it matches the expected tape technology evolution.