How does rsync file verification work?

[Moqi Ba]

Hello,

I want to use rsync to create backups. I think I need a verification that:
1) data is written to disk.
2) data is read back from disk.
3) verify the checksum of data.
Does the automatic file verification in rsync works like this? Technically,
I'd like to know how does we make step 2 read data from disk and not from
file cache/buffer in OS?
Or, do OS/harddrives always perform written data verification anyway so
step 2 is not really needed?

Thank you.
Moqi Ba
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