Backup MBR record — assuming your first disk is sda.

dd if=/dev/sda of=backup-sda.mbr count=1 bs=512

Backup partition setup info

sfdisk -d /dev/sda > backup-sda.sf

To Restore, just do the complete opposite (no count,bs)

dd if=backup-sda.mbr of=/dev/sda

Restore partitions just as simple (no -d)

sfdisk /dev/sda < backup-sda.sf