I don't know where TFA got the "globally addressable PB". I think someone was misquoted.
I can't find any mention of it in the NCSA webpages, and no shared memory system exists on this level, ccNUMA or otherwise (NASA Ames has a 4TB altix system, which is evidently the largest in the world that is publicly acknowledged).
Software distributed shared memory hasn't really gone anywhere either, so I think someone was fantasizing when they wrote the article... globally accessible filesystems, sure, but shared memory is something else altogether...
Another megabytes the dust.