Here is information on how to decode SCSI Sense Data.  This revolved around IBM Magstar products since that is where I was first exposed to the guts of SCSI errors.

Good reference was had from the 3590 Maintenance Information Guide, Msgs section.  This gives 90% of what anyone would need to decode SCSI LOG PAGE 06h messages for IBM tape drives.

Included within are how to decode SIM/MIM Records, Log Page 6, and other related information.  The 3590 Hardware Reference Guide, Appendix B also shows decent information in regards to non SIM/MIM errors.  It makes reference to sense key and ASC/ASCQ bytes.  You can acquire PDF copies of tape removable media storage systems' manuals via the following URLS:

	IBM Storage Reference
		http://www-03.ibm.com/servers/storage/tape/resource-library.html

	ASC/ASCQ Code Listing from the SCSI Technical Committee.
		http://www.t10.org/lists/asc-num.htm

The AIX Error Report records for TAPE_ERR# (usually 1-6) often include SENSE DATA in the Detail section.  A SCSI LOG PAGE 06h can be parsed manually to provide the SENSE KEY, ASC and ASCQ values, as well as the ERROR CODE which will tell us if it is current or past errors being reported.  An example Log Page 6 is below:

	0600 0000 0300 0000 FF80 0000 0000 0000 0000 0000 7000 0000 0000 0015 0000 000B 
	0000 0000 001C 7F00 2000 0033 7E58 0000 0000 0000 0000 0000 0000 0000 0000 0000 
	0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 
	0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 
	0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 B041 0000 0000 


If you'll notice, byte 0 is 06.  Also note that there are 32 bytes per line, and two hex digits per byte.

Byte 20 represents the SCSI error class.   Valid classes are:

    * 70 - Current Error (Direct Access Logical Block NOT From Sense Data).
    * F0 - Current Error (Direct Access Logical Block IS From Sense Data)
    * 71 - Deferred Error (Direct Access Logical Block NOT From Sense Data).
    * F1 - Deferred Error (Direct Access Logical Block IS From Sense Data).
    * 7F - Vendor Spec. Error (Direct Access Logical Block NOT From Sense Data).
    * FF - Vendor Spec. Error (Direct Access Logical Block IS From Sense Data).

In this example, EC (byte 20) is 70, which is valid and means this is a current error.

When the error class is valid, we can get the sense key from byte 22.

In this example, the sense key is 00 (zero) which means "NO ADDITIONAL SENSE".  The standard list of sense keys is:

	X0 - No Sense         X6 - Unit Attention    XC - Equal.
	X1 - Recovered Error  X7 - Data Protect      XD - Volume Overflow.
	X2 - Not Ready        X8 - Blank Check       XE - Miscompare.
	X3 - Medium Error     X9 - Vendor Specific   XF - RESERVED.
	X4 - Hardware Error   XA - Copy Aborted
	X5 - Illegal Request  XB - Aborted Command

ASC is at byte 32 (first byte on line 2) and ASCQ is byte 33.

The ASC and ASCQ chart is pretty extensive.  Please see the T10 webpage for an authoritative reference:

		http://www.t10.org/lists/asc-num.htm

Note also that sometimes the ASC/ASCQ pair you're looking up may fall under a different sense key than is expected.  The Sense key gives general information, such as "Recovered error", "hardware error", or the like.  The ASC/ASCQ pair tells what the actual problem is.  This isn't always 100% helpful, but is close.

The Magstar Maintenance and Ultrium SCSI Reference books makes reference to "Fault Symptom Codes" which are more definitive; however, due to confidentiality of the 3590 microcode, a complete list of fault symptom codes is not available.

For SIM/MIM records (Service Information Message/Maintenance Information Message), see IBM documentation:

		http://www-03.ibm.com/servers/storage/tape/resource-library.html

There are other ways to get this information, but this was easiest for me.

Yours truly,
Josh Davis