Unable to write to drive

[Marauder]

Hi all,

I have a problem that is driving me crazy. Hopefully I'm submitting this question to the correct place. 

My problem is... I have opened the drive /dev/ad0 with open("/dev/ad0", O_WRONLY) and it return's a valid file descriptor. The I attempt to write using the file descriptor returned. The write fails with errno=22 (EINVAL)

I have attempted to first open /dev/io with READ/WRITE access to see if that help's. No luck
I have attempted to lock the section of the drive I would like to write to with lockf. No luck

If anybody has any idea's or suggestions I would greatly appreciate them.

Thanx