/var/lib/pcp/config/pmchart/Diskbytes is in pcp-gui 4.0.1-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | #kmchart
version 1
chart title "Disk Throughput [%h]" style stacking
plot legend "Read rate" color yellow metric disk.all.read_bytes
plot legend "Write rate" color violet metric disk.all.write_bytes
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