I've been questioned many times by my server guys about putting backup servers on the same VLAN as the servers they will be backing up. I argue with IP CEF that the backup servers can be on a separate VLAN and still acheive the same backup speeds as if it were switched locally (same vlan).
What I would like to know is how much delay does IP CEF introduce (if any) vs locally switched traffic. Given that all servers are connected to the same Cat 6509 with Sup720's and 6700 series ethernet modules.
For most backups, even huge ones, net backup times should also be nearly identical. The reason being, any additional per packet forwarding delay just (mainly) shifts packet's arrival time, from sender; it doesn't really impact overall transfer time/rate.
This issue would be somewhat similar to having backup cross one L2 switch or 10 L2 switches. Each switch will add some latency, but assuming overall bandwidth isn't impeded, it will make little difference to overall transfer time.
For bulk transfers, usually the question is whether the platform supports the desired bandwidth transfer rate, not forwarding latency per packet. The latter only becomes important when dealing with latency sensitive apps.