I recently rsync'd around 2.8TB between a RHE server (jfs fs) and a
Netapps system. Did a 'du -sk' against each to verify the transfers:

2894932960 sources total, KB
2751664496 destination total, KB

That's a 140GB discrepancy. Subsequent verbose rsyncs have turned up
nothing that was not originally transferred.

I often note similar behaviour with smaller transfers between servers
with similar OS/fs combos and have always seen it to come extent with
transfers between systems of any type. It's just that the usual
discrepancies in this case are magnified greatly by the sheer volume of
data. Needless to say, 140GB going missing would be a bit of a problem
and it's not much fun picking through 2.8TB for MIA data.

Can anyone shed some light on why this happens?

tia