Spike in sync traffic similar to spike in wan/lan traffic, why?

[johns]

Why is my sync traffic similar to my WAN/LAN traffic (see image)?

In case it's not obvious, my setup is like this:  2 servers, 3 Nic's each…WAN connects to my upstream's switch (in a data center), my LAN connects to my local switch, SYNC connects to the second server via a cross over cable.

I started having fail over/carp issues, which I'll post about in another thread, but why is my Sync interface seeing 30 Mbps of traffic?

Thanks,

John

UPDATE:
How do I attach an image to this post?  I'm using the obvious method, but when I click save, I get the following error:

500 Internal Server Error
nginx

Image is 46kb, png format, I've converted to .jpg format but get the same error, I've also removed any whitespace in the filename, all to no avail.

UPDATE 2:
I cannot get the upload to work on these forums, so here's a link to the image:  http://imgur.com/RhvdNyW

[jimp]

Are those NICs physically related? (e.g. WAN/LAN are VLANs and SYNC is the untagged traffic on the interface)

Normally the sync traffic will roughly follow the other traffic since it will send state information (inserts, deletes, etc) but it wouldn't normally consume that much bandwidth.

But mixing of the parent interface and VLAN children and lead to some graphing issues exactly like what you're seeing.

[johns]

No, three different/physical NICs.  Making the issue even stranger.