While most modern PATA drives (circa 2000/2001) have the ATA security features included in their electronics, it is not clear to me how usable the atactl security commands are for the typical OpenBSD admin with PATA drives.
1. Many BIOSes issue a FREEZE LOCK on discovery, disabling security commands to avoid malicious attack. 2. Patch 1.43 to sys/dev/ata/wd.c added the FREEZE LOCK for OpenBSD during drive discovery by the kernel, and it's been in OpenBSD since 3.8. I discovered both of these things when I attempted to use atactl secerase on a drive, thinking it would be a convenient "offline" equivalent to dd. It and all security commands were aborted, leading me to look into it in a cursory fashion. Are you able to use these features? If so, are you getting around the BIOS or OpenBSD by cycling power on the drive after booting? Thanks!