What determines if initialization or syncing should occur based on the destination devices current state?

[CodeBradley]

I'm trying to figure out if the partitions need to be the exact same size as the destination disk or if they just need to exist in general? Having trouble identifying what determines which route to take.

Ultimately, I want rpi-clone to do an unattended setup on a new device and then add a third partition that I can use with CephFS (microceph) on an RPI 5 1TB NVMe SSD. It sounds like it would be better to partition the device first though to the sizes I want, adding the ~512MB FAT32 partition on nvme0n1p1, Rasbian on nvme0n1n2 (~500gb?) and microceph data on nvme0n1p3 (~500gb?). Reasoning being that it will save a ton of read and writes if I do the latter method.

[framps]

As far as I can see it's this code which detects whether an initialization should be done.

Source and target filesystem types are compared. If they are different and should be synced an initialization is done.