Linux bonding does offer the prospect of doing round-robin scheduling
of packets across the links in the bond, but that comes at a price -
packet reordering. Get "too much" of that and you start to get
spurrious retransmissions and clamping of the congestion window.

Also, the packet scheduling algorithms in the bonding code are for
transmit only. A backup server is ostensibly a recv-mostly sort of
thing. The scheduling of packets for inbound to the backup server
would be determined by the algorithms in the switch to which it was
connected.

You might also sniff the wire to see what sort of window sizes are
being used. Also, check the CPU util of _each_ CPU on the server.
I'm assuming your filesystem/whatnot can take-in data >> 60 MB/s? Does
the side sending the data to the server report any TCP
retransmissions?

rick jones
--
The glass is neither half-empty nor half-full. The glass has a leak.
The real question is "Can it be patched?"
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...