On January 1st 2013 ASTRON started the COBALT (COrrelator and Beamforming Application platform for the Lofar Telescope) project to develop a CPU-GPU based system as the central correlator and beamforming platform for the International LOFAR Telescope. The COBALT system is a co-design of both Commercial-Of-The-Shelf hardware components and ASTRON written software. The system consists of 8 production nodes and 1 development / test node, each consisting of 2 CPUs (Intel Dual Xeon E5) and 2 GPUs (NVIDIA K10) housed in a DELL T620 box and connected by an FDR Infiniband Switching network. This gives a balanced system where each CPU connects to one GPU, one Infiniband port and two Ethernet ports and both CPUs within one node are also connected. The cooling of the GPU cards in this set-up turned out to be an issue. Special air ducts were designed and constructed by the CIT Groningen en the ASTRON Mechanical Department, which provided enough cooling for the cards. The full system passed certification by DELL at the end of 2013.


Figure 1 One of the COBALT nodes.



The development of the software was based on existing research code in OpenCL for the correlator application, whereas the beamformed application was developed from scratch. The implementation was done in C++ and CUDA by a core team of four people making use of 3 weekly Agile / Scrum development cycles. This approach in combination with a focus on continuous integration and testing proved very effective. After careful commissioning the full system was production ready in April 2014.


Figure 2 The full COBALT system: 8 production nodes plus 1 test and development node.


Design: Kuenst.    Development: Dripl.    © 2022 ASTRON