Disk Write Caching Won't Stay Enabled After System Restart

I have two HDs in my system:

1. WD Caviar Blue 500GB (OS Drive)
2. WD Caviar Green 1TB

I've read that enabling write-caching may speed up drive performance. I checked on my 1TB drive, it was already enabled. On my 500GB drive though it was disabled.So I then decided to enable write-caching on my 500GB drive. I proceeded to do so without any apparent problems. However after doing a system restart I saw that it went back to being disabled again.I've tried this several times already, same thing each time!Enable write caching restart write caching disabled again.