* Darren Dunham <ddunham AT taos DOT com> [2006-03-31 10:37]:
> > We attempted to do this where I work using Sun Trunking v1.3 in order 
> > to increase the speed between our backup server and our data 
> > warehouse, which holds over 4 TB of data.  Sun Trunking will only 
> > work for increasing backup speeds if you are backing up multiple 
> > servers simultaneously.  If you are trying to increase speed just to 
> > back up one primary system, it will not work because all of the 
> > options in Sun Trunking are still based on MAC address - one trunk 
> > per MAC.  (Sun's engineers confirmed this for me.)  So, if you're 
> > looking to increase the speed between one server and your backup 
> > server, Sun Trunking will not do anything.
> 
> I'm not sure what you mean about all options being based on MAC.  Even
> starting with 1.0, SunTrunking has included a round-robin policy. 
> ( policy=2 )  But for a backup server I don't think that's a big deal.
> Because most of the traffic is incoming, it's the switch that is making
> the important decisions, not the backup server.  So it would have to be
> the switch that supports or doesn't support different link distribution
> options.
> 
> Even with round-robin, I wouldn't expect single-stream TCP performance
> to be incredibly increased.  But multi-stream performance should be
> better.  I've seen some documents warn about increased out-of-order
> packets occuring in this situation (because you're not forcing them to a
> single path), but the last time I was doing something like this I found
> round-robin to be the correct solution (it was direct attach multi-link
> with no intervening switches).  

The issue is that if you have two connections, only one will be used for
any given backup stream.  100Mbit + 100Mbit does not = 200Mbit, it means
there are two 100Mbit links that will share the same virtual IP.  if you
have a single backup stream that _could_ go at 200Mbit, the max speed
will still be ONLY 100Mbit, but two 100Mbit streams _might_ use the full
200Mbit (one on each), but there is no guarantee.  Generally, with
multiple backup streams the aggregate will be higher than the single
link, but rarely balances properly to fully utilize both and sometimes
bypasses using the second connection altogether.

-- 
David Rock
david AT graniteweb DOT com