CVMFS @Nikhef

Dennis van Dok

CernVM virtual workshop 2021, 1–2 February 2021

About Nikhef

  • High energy physics lab in the Netherlands
  • Sub-atomic physics, accelerator-based and astro-particles
  • "the smallest distance scale and the highest attainable energy"







Searching for dark matter

Einstein Telescope Pathfinder

R&D for testing and prototyping a new gravitational wave detector

Computing @Nikhef

Partnering with SURFsara to form a LHC Tier 1 since 2001.

Partnership evolved into a shared national infrastructure for large-scale science computing.

This is well beyond the scope of Nikhef's own mission, but strategically important for a sustainable computing infrastructure.

Recent usage numbers



CVMFS Servers

Stratum 0

We run a stratum 0 server for a long time and it is in need of an upgrade from CentOS 6 to CentOS 7. This is currently on-going.

The only repository of note that we have at the Stratum 0 is

Stratum 1

The stratum 1 server has been recently upgraded to CentOS 7. Icinga monitoring is in place, the system has a frontier-squid reverse proxy monitored by CERN.

We carry a bunch of repos from, and

On purpose we did not include the CERN repos.

The hardware is fully virtual, with a iscsi storage backend on a Fujitsu DX200 flexible tiering storage system. Not the ideal match, but it scales well enough so far.

Current disk use is 6.6TB, coming down from 11TB pre-upgrade. The difference is probably due to no garbage collection.

List of repos  

CVMFS Clients

  1. Grid cluster (~7500 cores)
  2. Local batch system (~800 cores)
  3. Condor cluster (new and growing)

Experience with using CVMFS at scale

Icinga sensor tracks every repository on every node.

Only occasional (mostly transient) warnings reported.

SERVICE STATUS: 1 I/O errors detected; repository revision 4958

Usually a manual cvmfs_config reload gets things unwedged.

Upgrade issue

On very rare occasions a system won't be able to recover from a CVMFS error and will need a reboot. These have been fewer with later versions of CVMFS.

Just recently the upgrade from 2.7.2 to 2.7.5 caused a handful of our worker nodes to hang; they needed to be drained and rebooted.

Osgstorage and stashcash

The repository is different as data is not public.

Requires use of x509 helper library and authenticated user.

Actual data coming from stashcache.

CVMFS 'for the rest of us'; users manage their own directories on this repository.

Presented at the meeting at RAL in 2016.

Co-developed with SURFsara.

Softdrive architecture


Implementation details

Nightly garbage collection (currently broken)

Nested catalogs for bigger users (and the monitoring user which triggered a revision every 5 minutes). This overcame the biggest performance hurdle.

Recently used to include unpacked singularity images (as a proof-of-concept).

Spider @SURFsara


Spider architecture

The Spider system at SURFsara is a high-throughput data processing platform, similar to Grid but with a broader scope and service offering.

Projects can port their software easily between Grid and Spider using

Users and use cases

SURFsara advisors have been helping applications to get their software onto different platforms with

  • minimise effort of (re)installing nad debugging when porting to a new platform
  • Centralise management of software used at different sites
  • Spreading of singularity images
    • monolithical
    • unpacked

Notable projects:

  • Tropomi (tropospheric monitoring) uses it to distribute binaries to different platforms.
  • LOFAR-SKSP (Solar physics and space weather)
  • ProjectMinE (ALS research).

Future outlook

Upgrading the Stratum-0 immediately.

Explore the possibilities for unpacked container images, template transactions, and the ephemeral writable shell.

Keeping things going with minimal effort.