One of the things that imo has pushed some of the other Unixes out of HPC is the move to using cluster file systems. Any Unix supports a traditional NFS-mounted NAS solution for storage, as used to be typical in HPC clusters (and still is fairly common in smaller installations at universities). But only AIX and Linux really have solid cluster filesystems; there's nothing in the BSD world analogous to IBM GPFS, or to Lustre, and porting is nontrivial.