Re: Looking for recommendation on 10G Ethernet switch

[Nick Hilliard <nick () foobar org>]

On 02/11/2012 20:10, Jeff Wheeler wrote:
> The biggest difference between the TOR-style switches and chassis
> offerings, aside from the obvious, is buffers.  All the TOR-type 10G
> switches have really small buffers and that can be a performance issue
> for iSCSI when utilization is high

not particularly when utilisation is high, but in situations where
congestion occurs, e.g. when you either have a high write load from
multiple clients to a single server, or if you're down-shifting from a 10G
server to 1G clients or something.

> The vendors will all tell you about lossless ethernet, flow control,
> etc. and that crap sounds great on paper.  Try making it actually work.

flow control on a switch port can lead to hol blocking, which is bad bad
news - guaranteed to trash multi-access network performance.  Some vendors
actually push this as a feature.  I don't completely understand why, but
maybe it has something to do with customers mistakenly believing that it
will make their lives better.  People believe in all sorts of odd
superstitions though: black cats, spilling salt, having full features on
ethernet LAGs, vendor marketing blurb, fear of the number 13, etc.  All
very odd stuff.

Nick