This is a followup question to Cannot mount /dev/sdc1 on Debian 5.0, special device /dev/sdc1 doesn't exist

Basically, I have 6 SATA hard drives in a machine and I'm trying to create a RAID6 array with them. When I try to run the mdadm command to create (with the verbose option) a raid array, I see messages like "mdadm: super1.x cannot open /dev/sdf1: No such device or address" which are resolved by doing partprobe /dev/sdf and then re-running the mdadm command.

The problem is that I have to run partprobe after each reboot, and from experience I don't think this is normal behaviour -- on no other linux machine do I have to partprobe the device before I can use it. Something must be going wrong, but how do I troubleshoot this to find out what? Could this be caused by a hardware problem?

Edit: Additional note - before I seemed to only have this problem with one drive, but now I'm having it with 3 drives.