At our organization, we're looking at implementing some sort of informal internal policy for server maintenance. What we're looking at doing is completing maintenance on our entire server pool every two months; each month we'll do half of the servers.

What I'm trying to figure out is some way to split the servers into the two groups. Our naming convention isn't much to be desired (but getting better) so by name or number doesn't really work.

I can easily take a list of all the servers and split them in two, but with new servers are being added constantly, and old ones retired, that list would be a headache to maintain. I'd like to look at any given server and know if it should have its maintenance done this month or next.

For example, it would be nice to look at the serial number. If it started with an even number, then it gets maintenance done on even months and vice-versa. This example won't work though as a little over half of the servers are virtual.

Any ideas?