Contrary to the user manual, --comment parameter is not accepted by VBoxManage addiscsitarget subcommand.
VBoxManage addiscsidisk --server storage --target longtargetID --comment "test comment"
VirtualBox Command Line Management Interface Version 3.0.0
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All rights reserved.
ERROR: Method SetDescription is not implemented
Details: code NS_ERROR_NOT_IMPLEMENTED (0x80004001), component HardDisk, interface IHardDisk, callee nsISupports
Context: "COMSETTER(Description)(comment)" at line 1052 of file VBoxManageDisk.cpp
iSCSI disk created. UUID: longuuid[[BR]]
Beside this, as the output shows the disk is created and working properly. I do not know how you intent to show this comment in the media manager interface, but giving an option to show an alias name to iscsi discs would be nice. (I cant choose more host type, but I experienced this on OpenSolaris? and OS X Leopard also.)