I like to use the cheatcode tohd to put the knoppix dvd onto the hard drive. However, I didn't use mkimage when I ran it initially. (I don't know if that would make a difference)
For some reason, using the cheatcode "mkimage" later was ignored.
My boot command line was something like this:
knoppix64 tohd=/dev/sda1
and it dutifully created the KNOPPIX directory on /dev/sda1 but I didn't get a persistent storage file.
One thing that's interesting is that when knoppix boots it automagically scans the drives and finds that KNOPPIX directory even if I don't specify the cheatcode "fromhd=/dev/sda1".
So if you want to create that knoppix-data.img by hand just launch a terminal after booting into your KNOPPIX and
dd if=/dev/zero of=/mnt-system/KNOPPIX/knoppix-data.img bs=1024K count=4000
This will make a 4000MB persistent file (you can make larger if you like) The hard drive that I'm using is formatted FAT32 so my limit is 4GB. Using other formats will have no such restriction.
(And as always, exercise care with dd since you can easily clobber your drives if you enter the wrong parameters. They don't call it disk destroyer for nothing. I've done it once or twice by entering parameters without thinking.)
Then you need to format it
mkfs.ext2 /mnt-system/KNOPPIX/knoppix-data.img
(You may need to use a -F parameter to "force" it to use a regular file, since it normally expects block devices)
(For some reason I thought it had to be reiserfs, but ext2 seems to work. I kept formatting it as reiser and it wouldn't use it)
Also, if you don't like the messages about KNOPPIX-DATA when you boot, there's a file called "knoppix-data.inf" that you can rename. It will mount a persistent PARTITION, and since we're using a persistent FILE, we don't really need it. The error messages don't hurt anything, but if you rename that file, you won't see them anymore. You can always rename it back to the original name.
mv /mnt-system/KNOPPIX/knoppix-data.inf /mnt-system/KNOPPIX/was-knoppix-data.inf
IBM Power S822 8284-22A 12SFF Power8 3.89GHz 6Core 64GB RAM No HDD Server System
$359.99
1U IBM x3550 M5 4 Bay SFF SAS3 Server 2x E5-2683 V3 28 Core 128GB DDR4 2x Tray
$318.00
IBM Power S822 12-Bay Server System Power8 Core 3.42Ghz DVD-Rom Drive 64GB No HD
$349.99
IBM Power S822 8284-22A 12SFF Power8 3.89GHz 6-Core 64GB RAM No Bezel/HDD Server
$319.99
IBM 8286-41A iSeries Power8 Server
$1149.99
IBM mainframe server cpu IBM93 vintage cpu collector's item
$129.99
IBM Server eServer | IBMR1000 | UPS 1000VA 700W W/New Batteries
$115.00
IBM System x3250 M4 Server Intel Xeon E3-1220 3.10GHz 8GB RAM No HDDs
$60.56
IBM System X3650 Server M2 2 x Xeon X5570 2.93 Ghz w/128 GB/DVDRW
$152.95
IBM System X3250 M3 Server 8GB RAM Intel Xeon x3440 2.53ghz (NO HDD)
$41.99