I buy from the same vendor but will buy in different orders, I.e. I'll buy half the disks as soon as I know what we are doing and then buy the other half installed in the machines a month or two later,
or ill buy the machines with half the drives, build out the product them buy the other half of the array and slap it in a couopke days before go live.
I've also hit a few specific firmware bugs in drives, my favorite was a 49 day uptime bug related to a 32 bit counter.
Its one of those awful ops problems :)