Change your fstab. The usage of the variable device nodes like
/dev/sda is discouraged now.
Look at your
/dev/disk/by-id/ directory. Mine looks like this:
> ls /dev/disk/by-id/
There you have your disks including serial numbers. I have a SATA hdd and an USB card reader here.
You can use these links in your boot loader and in
/etc/fstab unless your distribution is ancient.
There are also /dev/disk/by-uuid/
Ah, and don't forget the boot loader. If
sda is also the first disk
0x80 that the BIOS sees, you might not have one installed on