Why does Plesk show errors for /dev/loop partitions?

Question

Why does the Tools & Settings > Server Information page show errors for /dev/loop  partitions and warns that they are 100% full?

Answer

/dev/loop partitions are loop devices making plain files accessible as block devices. They are typically used for mounting disk images and are read-only, so 100% disk usage is expected for them.

Warnings for these partitions have no effect on Plesk functionality and can be ignored.