Acho que o artigo do My Instance is Booting do AWS EC2 User Guide do volume errado é uma resposta detalhada à sua pergunta. A ênfase é minha.
In some situations, you may find that a volume other than the volume attached to
/dev/xvdaor/dev/sdahas become the root volume of your instance. This can happen when you have attached the root volume of another instance, or a volume created from the snapshot of a root volume, to an instance with an existing root volume.This is due to how the initial ramdisk in Linux works. It will choose the volume defined as
/in the/etc/fstab, and in some distributions, including Amazon Linux, this is determined by the label attached to the volume partition.
E a correção em resumo:
Use the
e2labelcommand to change the label of the volume to something other than/.[ec2-user ~]$ sudo e2label /dev/xvdf1 old/