mpiCASA.md

[Graviton28]

Rewrote mpiCASA.md from scratch. It was previously raw, unfinished draft notes: a fake placeholder path (/users/sbruzew/xena-scratch/casa-blah-blah/bin/casa), dead PBS ($PBS_NODEFILE), a nonexistent singleGPU partition, and unresolved rhetorical questions to self.

Investigated live on Easley. CASA 6.5.2 is genuinely installed and works, but hit a real infrastructure bug along the way:

module avail casa / module spider casa both report casa/6.5.2 as loadable ("This module can be loaded directly: module load casa/6.5.2"). Actually running module load casa/6.5.2 fails:

Lmod has detected the following error: These module(s) or extension(s) exist
but cannot be loaded as requested: "casa/6.5.2"

Re-checked with the cache disabled (module --ignore_cache avail casa) and there is currently no live modulefile for CASA at all — Lmod's cached spider index is stale and advertises a module that doesn't actually exist anymore. This is a known limitation, not a doc bug — flagged in the doc itself with a pointer to help@carc.unm.edu, same as how the unresolved simcov/hwloc issue was handled in #284.

The underlying CASA 6.5.2 software is still present and world-executable at a fixed path (/opt/local/casa/6.5.2/casa-6.5.2-26-py3.8/bin/), so the rewritten doc uses that direct path + alias instead of module load. Tested end-to-end on Easley via srun:

• casa --nogui --log2term -c hello.py (1 task, debug partition) — ran a real Python script inside CASA, correct output.
• mpicasa -n 2 casa --nogui --log2term -c hello.py (2 tasks, Slurm placed them on 2 separate nodes) — both ranks correctly executed the script. (There's a benign mpirun has exited ... exiting improperly message at the end even on success — CASA's script mode doesn't call MPI_Finalize() cleanly; documented this as expected, not a failure.)

Also replaced the fake singleGPU partition with Easley's real partitions (general, bigmem, h100, l40s, interactive, debug, scavenger — verified via sinfo), and PBS_NODEFILE with plain Slurm --ntasks.

Test plan

• Confirmed module load casa/6.5.2 fails and diagnosed root cause (stale Lmod cache) on Easley
• Confirmed direct-path casa binary runs (--version, and a real script via -c) on Easley via srun
• Confirmed mpicasa -n 2 runs the script correctly across 2 nodes on Easley via srun
• Verified real Easley partition list via sinfo