CDB "EF 00 00 00 00 00" - iSCSI???

Mike Berhan mikeb at
Mon Jun 23 07:12:54 PDT 2003

* From the T10 Reflector (t10 at, posted by:
* "Mike Berhan" <mikeb at>

I am seeing the CDB "EF 00 00 00 00 00" being sent to the hard drives on a
Windows 2000 test system (I do not have the system; I have been given the
software trace).  This CDB isn't defined in SPC or SBC as far as I can tell.

For the ATA drive on the system, it fails.  However, for iSCSI devices, it
is working.  The SCSI miniport driver is the "IBM iSCSI Client for Windows
Device Driver" and the drives attached to it accept this CDB and return
eight bytes of data.

In talking to the actual iSCSI device vendor, they indicate that they do not
accept this CDB.  If this is true, this "could" indicate that this is some
means of private communication between utility software and the IBM iSCSI

My question is the following for those familiar with iSCSI.  Is this CDB
something proprietary to say an IBM driver or something that all iSCSI
driver developers are using?  Is it even related to iSCSI?  Has anyone ever
seen this CDB before or know of a specification that describes it and the
return data?  If it helps any, here is some sample return data:

9C C8 11 AC 00 00 00 CC

Thank you in advance.

Mike Berhan
mikeb at

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