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