My method was, having flashed an image to my original Kingston Class 4 8GB card, to then put it in the Pi, run it for a while, including writing programs and updating/upgrading my system, then shut down and copy the card as an updated image, in case anything went wrong. It worked fine for a few months, then the writing of the new image failed after about 3GB, then at 1.5Gb. Posting elsewhere got replies suggesting that:
a) the Pi's voltage was wrong, or
b) the cards (both of them!) were shot.
The voltage checked out (under load) at 4.89 - 4.95V, so I bought a new card. As Class 10 cards are competitively priced, I went for a Sandisk C10 8GB. I flashed my latest good image to it, put it in the Pi, downloaded software updates, shut down, copied the new image to my PC. So far, so good – a Class 10 is definitely faster than a Class 4! I then came to flash the new image to one of the old C4 cards – and it failed ‘Not enough space’. Whaaat!!! Sure enough, when I compared the new image with some older ones, it’s 100+MB bigger …! I use Win32 Disk Imager. Any ideas as to why a 7,639,040KB image that gets written to the Sandisk C10 comes back as a 7,761,920KB file?