SD card shrinks in allowable size after copying disk image

Solution 1:

When you copy a raw disk image to the card, you copy the partition table with it. In many images, there is one small partition (to fit into all media) and the remaining space is simply unallocated – you can create a second partition there, or extend the first one.

Unfortunately, Windows does not support multiple partitions on removable drives and disables the usual management functions. There's still a way to fix your card:

• Boot into a Linux live CD (Ubuntu is okay), then use GParted or command-line parted to resize or create partitions.

• Alternatively, if you don't mind losing all data, you could use dd or a similar tool to completely zero out the partition table (first 512 bytes); after this, Windows will ask to "format the disk" creating a new partition in the process.