pi-man-uk wrote:2) Copy the filesystem as an "image" to an external location, sounds like this is slower.
I'll have to try this out. Did I broadly understand it correctly?
Will be considerably quicker if you pipe the output through gzip with max compression (gzip -9), since it will squash unallocated space down to pretty much nothing. DD will read the entire card, (which it will do no matter what method you use), but the output file will be very compressed.
If you have been really busy on the SD card, which will leave file fragments in unallocated space, you can 'wash' the unallocated space with:
dd if=/dev/zero of=bob.file
This will create a file filled with zeros until there is no unallocated space left on the disk, and dd just halts with a "No space left on device" message. Simply delete "bob.file" and that file becomes unallocated.
To be honest though, you would be better off chucking the card into a reader on your computer and dumping the entire card out to a file. If you keep working on the Pi whilst it is imaging, (or some other process/daemon is really active) you could end up corrupting the resulting output file, since activity will be changing the card contents as it's imaging. This includes any swap space if you plan to image the entire card at the block device level (/dev/sda vs /dev/sda1)