Linkagg does not only give failover but additional bandwidth as well, but you need to be aware, that a single Connection (e.g. a flow between a backupserver and a storage) will only take one of the lacp links, hence has a bandwidth of 10G (link). If you have multiple flows using the lacp you can expect a even distribution using both links.
If you need more bandwidth for a single connection you have to switch to 40G.
But this applies to all vendors (afaik except Brocade VCS
http://blog.ipspace.net/2011/04/brocade ... rfect.html) and does not apply to servers.