efficiently synchronizing source and destination

[Kevin Karwaski]

All,

I have two fat32 formatted external drives (on the localhost) that
need sync'ing. Each of the drives contain different files. The end
result I'm looking for is two identical disks.

My question is whether or not I can encapsulate this process in a one
liner with rsync or if i need to make two independent calls to rsync
as follows:

rsync -av /path/to/source /path/to/dest && rsync -av /path/to/dest
/path/to/source

In the situation above, the dest has files that do not exist on the
source, hence the second call to rsync...

Any input or suggestions would be greatly appreciated... Thanks!

-- 
Kevin Karwaski
kkarwaski<at>gmail.com