Tricity

I am stymied where I shouldn't be.

I have this ematic eGlide 2.2 e-book reader with the nefarious RK2818 chipset. This means that I cannot permanently root it unless I re-flash the ROM. Of course, I want to back up the old ROM before proceeding. So here is what I tried:

1) Use SuperOneClick to gain root through psneuter. WORKS!

2) The expected: mount -o remount,rw /dev/block/mtdblock4 /system

Fails -- because /system is a cramfs file system, and thus always R/O.

3) The unexpected: cat /dev/block/mtdblock4 > /sdcard/mtd4_system.img

As root, I can naturally access /dev/block/mtd*, but the copy process stops when the sdcard is full (4GB), although I *know* that mtd4 has only 272 MB.

4) dd if=/dev/block/mtdblock4 of=/sdcard/mtd4_system.img

Same effect. Can anybody point me in the direction of why the copy process doesn't stop at end-of-file?

Much appreciated!