writev to SCSI disks: Does sg work?

Hi!

I was wondering if I did a simple writev to a SCSI disk, does it take the sg path to the device? I am guessing this sg (REQ_SPECIAL) is only true for character devices (and ioctl's) and not block devices.

These are my questions:
- Is sg a common feature among SCSI disks these days? How do I know
what disks support this feature?
- How does one make writev work for SCSI disk (as a block device)
in direct_io?
- If I use SCSI disks as character device, can I use writev on the
character device file, and will sg codepath be taken?

Thanks
Dheeraj