The AOC has 30 sixteen core cluster nodes which jointly provide roughly 4Million core hours / year. SE Continuum imaging takes between 30M and 60M core hours / per year (50M to 100M per 18 months). To realize operational scale imaging the NRAO needs to identify 10 to 15x its current capacity.
VLASS SE imaging in its current form presents 3 unique challenges to external processing facilities
- Input data sizes are large
- Calibrated MS is ~1TByte for most SBs: could be reduced to 8GB by pre-splitting the MS to relevant visibilities
- CFCache is 30GB: could be generated on the fly at a minor run time cost (for monolithic imaging)
- CASA code stack is ~1GB (may only be an issue for more fine grained decompositions)
- Memory foot prints are large
- Need to characterize major minor cycle
- Need to examine CASA 6 refactored imaging code in this context
- Imaging run times are viewed as long
- Single node 16x parallelization runtimes are in the 200 to 500 hours wall clock time. For external facilities without pre-emption wall clock is important
All 3 areas can be addressed by decomposing the external processing request from a full pipeline execution to a portion of the imaging step. Possible areas of decomposition are:
- split workflow in to separate data staging and imaging pipelines to avoid manipulating 1TB class MSes
- per tclean call (scripted pipeline has 12 unique calls to tclean)
- per major cycle (submit jobs on a per major cycle basis) (assuming 400 our jobs with 20 major cycles this results in ~10 hour jobs from external host perspective)
- Separate major and minor cycles (run major cycle on external hosts and minor cycle locally to more effectively balance memory demands)
- Separate major cycle per SPW
- reduces input data and CFcace input size by 16x
- reduces per job runtime by additional 16x