SMEM will increase the size of the SMEM partition of the SCRATCH DBSET. However, if you are filling a disk then increasing SMEM is probably not going to help unless your machine has an enormous amount of physical memory.
For example, if you machine has 64 GB of RAM, You could probably run NX Nastran with mem=48GB (leaving 16 GB for the OS, other processes, etc.
If your large analysis requires 10GB of memory to avoid spill, then you could set SMEM=32GB
This would make your total scratch space 532 GB (assuming that the 500 GB scratch drive was empty to start with). This is less than 10%
You will probably have to split the SCRATCH DBSET across multiple physical drives. This can be done using the INIT and ASSIGN FMS commands.
See this Solution Center article for more information: