Backup the disk partition table on /dev/sda.
dd if=/dev/sda of=sda.mbr bs=512 count=1
It’s also useful to keep a human readable copy of the disk layout for future reference.
sudo fdisk -l > partitions.lst
Recover your file system using your partition table backup.
dd if=sda.mbr of=/dev/sda bs=512 count=1
NOTE: This is a nice way to keep the information about your file system and will it help you in the future if you get disk corruption.
This does not only apply to linux partitions but all types of partitions.