When disks have exactly the same brand and type (this is quite normal on virtualisation platforms) Linux can mess up the logical assignment of these disks and swap, for example, sdb1 and sda1 after a reboot. To solve this we need to mount those disks based on their UUID.
Use the following command to retrieve the disk UUID:
blkid
Result:
/dev/sdb1: UUID="c924eac3-eb44-453e-8eb3-e9c8c8afebc0" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="f61232c6-01"
/dev/sda5: UUID="64fbe892-0cb1-4854-87ee-775dea97f60d" TYPE="swap" PARTUUID="cfd518f5-05"
/dev/sda1: UUID="c2f61b6b-4f90-48b7-a823-2b0a6863eb6e" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="cfd518f5-01"
Determine which disk you want to mount and adjust /etc/fstab accordingly:
UUID=c924eac3-eb44-453e-8eb3-e9c8c8afebc0 /data ext4 defaults 0 0