Disk device changes after each rebooting

"Using UUID is always the better option. But that being said your problem comes from you uDev. Some older Sata controllers take a bit of time to spin up and by that time udev has already found the IDE drive and used it as the first drive. Although I do believe this is only from Cold-Boot.

When working with Coreboot I ran into this problem often and the only real solution I every found was the pause the system for a few seconds (My 1TB took anything up the 20secs) to allow the drives to spin up.

Hope it helps in someway!"

I agree with the previous comments about using UUIDs instead of /dev/sdX in your configurations (such as in /etc/fstab). Although this is an old question, I thought I'd share this page I found when dealing with a similar problem today. It seems to be a good reference for how to use UUIDs (or labels, if you prefer those).