[Simh] vms 5.5-2 cdrom format

[Lu, Mark]

Hi, hope this hasn't been covered before...
does anyone know whether i can create an "iso" image from my VAX6000 5.5-2 "VMS Consolidated Software Distribution" CD#1 to install VMS with simh on linux?

i tried 
dd if=/dev/cdrom of=cd.iso
which seemed successful.
but following the procedures in http://www.wherry.com/gadgets/retrocomputing/vax-simh.html to boot dua3 gave me the following error
-DUA3
?42 NOSUCHFILE, DUA
HALT instruction, PC: 00000C1A (MOVL (R11),SP)

i am not sure what the difference between iso9660 format and ODS-2, but i could not see CD contents with win2k itself, but was able to read the CD using http://vms.process.com/ftp/vms-freeware/fileserv/ods2.zip . So is using dd the way i did the right way to create a "drive file" that can booted by simh?  Thanks.