Hi, utu. I wish you a happy new year, too.

The size of the large KNOPPIX file on the DVD is 3900339847 bytes (3.6 GB).
The size of the large KNOPPIX file on the CD is 681.7 MB.
I have got a 4 GB USB flash device with a capacity of 4110417920 bytes. If I would install the Knoppix 6.2.1 DVD on that USB Flash drive, there were less than 200 MB free for the persistent store. 200 MB is the minimum size for the persistent image. Therefore you need a really large flash drive if you want to install the Knoppix DVD instead of the CD and use a persistent store.