Simple Question

[David Vincent-Jones]

I have been using rsync on my laptop for some time to safeguard an
extensive image collection.
My usage has been: .. rsync -av --delete ~/Pictures /media/disk
I have found this exceptionally fast ... just as advertised!

I now have set up a new computer system where I want to back up my /home
to a sata drive.
My phrase for this is: .. rsync -av --delete /home/david /media/Sata
Which appears to be identical to my earlier usage .. but .. rsync
appears to be totally rewriting the backup and instead of being able to
get a quick refresh, the backup is now taking an hour or more.

Any idea what is going on?

David