Look at this link:
http://www.mombu.com/microsoft/windows-programmer-nt-kernel-mode/t-howto-send-ata-spec-command-to-usb-hdd-1646752.html
Q: howto send ATA spec. command to USB HDD?
A: You are limited to whatever the USB->ATA tailgate (bridge) chip supports.
If you control the bridge, you can implement whatever you want. If you
don't, you'll have to ask the bridge vendor to reveal what they do support.
See my replies in the thread on 1394->ATA on NTDEV for more information.
Q: Once more question: whether probably to get access to everyone disk
in SCSI RAID?
A: No.
You can only send SCSI commands to the bridge/enclosure at the end of the USB
cable. How they are translated to ATA commands - is not under your control.
I assume El Cheapo enclosures to only translate the essential SCSI commands. In
this case, you will only have 1) SCSI INQUIRY emulated by ATA IDENTIFY 2) SCSI
READ CAPACITY emulated by ATA IDENTIFY 2) READ and WRITE 3) VERIFY.
And that's all. In this case, you will have zero chances sending any
non-trivial ATA commands, since the USB-to-ATA bridge on other side provides no
ways of doing such.