The Netprobe uses the function statfs() to gather this information about specific mounted file systems.
The value of totalSpace of disk shown in Disk sampler is based on the total value of "Used" & "Available" columns and not from "1K-blocks" as it might be expected.
df command output:
In this example, we are looking at the /boot partition on a Linux machine.
Disk sampler dataview:
Please also note that the total value of "Used" & "Available" columns might not be equivalent with "1K-blocks" column due to blocks that are reserved for root.