Well....this all worked marvelously, but it didn't.
I spread my 18 subsets over 3 machines with Xeon processors, started the batches last night and I came in this morning and voila they were done. Didn't believe it could work so quickly and sadly, it didn't. The results in the OD Cost Matrix table look correct (I've only tested a few as of yet), however, it didn't solve for all the Origins. I had subsets of 50,000 origins and in one set, it only solved the first 1,443 origins, in another the first 9000 - and these were run on the same machine, in the same batch. The OD Cost Matrices ended up with vastly different numbers of rows. For example, in one batch, one matrix had 6,594,231 rows, another 1,021,000 and 155,000 (there were 2 more in this batch that I haven't looked at yet).
I'm doing all the processing in file geodatabases, one for each subset, so I don't think I'm bumping up against any size limits. Each GDB is in a separate folder - although all of these folders are subsumed in one folder.
I have 48GB of RAM and gobs of harddrive space, so I don't think that is the issue.
Anyone have any idea what is going on? Or how I can log error messages so I might have a clue as to what is going on?
Thanks,
Heather