Highlights of CTA Day at the 6th EOS Workshop

Thank you everyone for your contributions to yesterday’s CTA Day at the EOS Workshop!

Thanks to you, we were able to put on a varied programme with lively discussions. There were over 100 participants. It’s very encouraging for us at CERN to see the growth of a dynamic community around CTA.

We look forward to next year’s workshop, which we hope will be a return to meeting in-person, allowing the networking and ad-hoc meetings which we have missed during the last couple of years.

I have summarised the main workshop contributions below. The sessions were recorded and the recordings will be added to Indico within the next week or two.


  • The CTA project, team and community. Oliver Keeble opened the CTA Day with an introduction to the CTA project, the people working on it and the wider CTA community.
  • CTA Status and Roadmap. Michael Davis gave a status report on the CTA software and the planned direction of software development efforts for 2022 and 2023.

Site Reports

  • CTA at AARNet. Denis Lujanski gave an overview of the CTA deployment at AARNet, which has been in production since late 2021. Helm (and Rook) is used for deployment. AARNet have deployed a backup service based on Restic which is being made tape-aware.
  • EOS and CTA Status at IHEP. Yujiang Bi explained IHEP’s plans to migrate their tape software from a customised version of CASTOR v1.7 to CTA. Archival services are already using CTA. Files in CASTOR are being migrated by copying the files (will finish 2022-23).
  • CTA at RAL. George Patargias presented RAL’s successful migration of Tier-1 tape storage from CASTOR to their new EOSCTA instance, called Antares. The presentation includes details of CTA configuration, the migration process, and testing to ensure readiness for upcoming data challenges/LHC Run-3.

Technical Presentations by the CTA Team/IT Storage Group

  • How to enable EOS for tape. Julien Leduc explains the important EOS configuration options to consider when adding CTA as the tape back-end.
  • Configuring user access control in CTA. Volodymyr Yurchenko explains how EOS access control options (POSIX permission bits and ACLs) and CTA mount rules interact to control access to files stored in CTA.
  • Tape Drive Status Lifecycle. Jorge Camarero Vera presents the drive states and state machine enacted by CTA tape drives during data transfer sessions.
  • EOSCTA file restoring. Miguel Barros presents how disk and tape file metadata can be restored in case of accidental file deletion.
  • Maintaining consistency in an EOSCTA system. Richard Bachmann gives an overview of the tools, workflow and monitoring to check that EOS disk file metadata and CTA tape file metadata is consistent.
  • An HTTP Rest API as SRM replacement for tape access. Cédric Caffy reports on the CERN implementation of the common HTTP REST API for “stage and transfer” operations, and gives a live demo which compares the XRootD and HTTP protocols.

Evaluation of CTA

CTA Tape Back-end Discussion

The CTA Day closed with a Birds of a Feather session on CTA tape format support. The Fermilab and DESY use cases require that CTA will offer read (but not write) support for their existing tape formats (based on CPIO). This is necessary to allow migrating to CTA without the need to physically copy all of the exisiting tapes.

DESY have proposed changes to the CTA “retrieve” protocol and tape server to allow reading tapes which are not in the native CTA/CASTOR format. During the BoF discussion, these changes were accepted in principle. Integration of DESY’s work into CTA will be added to the CTA development roadmap.