Thanks for the answer Joshua.  It looks like sg0 and sg1 are drives
and sg2 is the changer, mtx -f /dev/sg2 inquiry returns:

Product Type: Medium Changer
Vendor ID: 'EXABYTE '
Product ID: 'Exabyte EZ17    '
Revision: '1.11'
Attached Changer: No

But mtx -f /dev/sg2 unload says

Unloading Data Transfer Element into Storage Element 1...mtx:
Request Sense: Long Report=yes
mtx: Request Sense: Valid Residual=no
mtx: Request Sense: Error Code=70 (Current)
mtx: Request Sense: Sense Key=Not Ready
mtx: Request Sense: FileMark=no
mtx: Request Sense: EOM=no
mtx: Request Sense: ILI=no
mtx: Request Sense: Additional Sense Code = 04
mtx: Request Sense: Additional Sense Qualifier = 8E
mtx: Request Sense: BPV=no
mtx: Request Sense: Error in CDB=no
mtx: Request Sense: SKSV=no
MOVE MEDIUM from Element Address 82 to 1 Failed

and amcheck returns:

amcheck-server: could not get changer info: get ElementStatus

I'm using chg-scsi as my glue, thanks much.

Steve