Unfortunately sometime one has to rsync directories between too different filesystems.
E.g., [V]FAT which is widely used on USB sticks and external hard drives, has a 2-second granularity for timestamps and does not support unix's owner+group system.
Here are the rsync options that can make one's life much easier in such situations:
... increases the granularity of timestamp comparisons (actually
=1 should do) and avoids very much unneccessary traffic at the second run and any further run.
Btw., rsync really should detect such situations automatically, at least locally.
... suppresses error messages meaningless on FAT respectively.
It's also recommended on SMBFS/CIFS and NTFS, because those know owner attributes but usually use different user+group databases.
From: IBCL BLog.
Originally posted: 2008-07-19