Re: Flow control for iscsi
Massimo Rosen
zenking wrote:
>
> Should I enable flow control on my NW6.5 SP8 initiator servers with
> B57xx NICs connected to switches and EQ san that support flow control?
It shouldn't matter at all, assuming all your gear is gigabit, which I
assume. ;) FlowControl is generally only important when there's a speed
chnage between devices. E.G, when you connect a 100MBit Workstation to a
Gigabit server. In that case, something has to throttle the gigabit
server, and that's the job of flow control.
CU,
--
Massimo Rosen
Novell Product Support Forum Sysop
No emails please!
http://www.cfc-it.de
Massimo Rosen
zenking wrote:
>
> Thanks for the responses. I see that TCP has its own flow control and
> enabling FC on the switch ports could cause problems, even in mixed
> environments
No! TCP flow control and ethernet flow control are totally unrelated.
> (ours is full gigabit setup). Here are a couple of posts I
> found if you're interested.
> 'Virtual Threads: Beware Ethernet flow control'
> (http://virtualthreads.blogspot.com/2006/02/beware-ethernet-flow-control.html)
> 'Ethernet Flow Control'
> (http://www.29west.com/docs/THPM/ethernet-flow-control.html)
Don't believe everything you read on the Internet. ;) I only started
reading the first link, and the real important sentence in it is "I
don't know much". It's just another example of people with some nice
dangerous half-knowledge feeling the need to let the world take part in
it.
Massimo Rosen
zenking wrote:
>
> *No! TCP flow control and ethernet flow control are totally unrelated.*
>
> Isn't that what he's saying, that because flow control is already built
> into the tcp protocol at its layer (data?), that it's generally bad to
> implement it on another layer, in this case transport?
Totally not. Lack of ethernet flow control potentially leads to packet
loss followed by retransmissions.
TCP flow control doesn't deal with packet lossage. Losing packets is
*always* bad, you would never ever want to have that happen. Ethernet
flow control in *NO* way interacts or hurts TCP flow control, the
opposite is true.
> By the way, any thoughts on STP? We have 2 switches for redundancy in
> our setup. I'm planning to connect them directly and disable stp for all
> ports except the ones for the direct connection. Sound right? Thanks for
> the insights.
Yep, that's right. In a perfect setup, you only want STP active on ports
connected to other infrastructure, but never on ports connected to nics.