[Mashiro]

Your KVM VPS uses virtio drivers for the disk and those disks in that case all are to be found at /dev/vdX (x = a,b,c...) and the partitions are at /dev/vdXY (y= 1,2,3...).

You have /dev/vda1 which however is just the boot partition. So maybe rather use the LVM root partition to do the tests which is "/dev/mapper/centos-root". Your OS installation uses LVM rather than classic partitions.