>>> Did some research and found this sometimes occurs when the >>> speed of the server nic is so much faster then the client nic. >>> Apparently this showed up with the 2.6 kernel. > [...] >> Could not find where I saw the original write up. But it has to >> do with the NIC in the server box being 1G and the NIC in the test >> laptop being only 100MB. > > >I suspect that such mismatches are not the problem, because the >fact that *any* bits are flowing means that a whole bunch of >low-level plumbing is working properly.
Not at all! In my NFS on Tru64 Unix days, I was horrified at some of the abysmal buffering on some top of the line Gigabit Ethernet switches. A typical box could buffer 350 KB, i.e. 2.8 Mb, and that is about 3 msec of GbE wire time. Silly me figured a switch could buffer at least a second's worth of data before discarding data, maybe 100 msec at worst. I would love to get my paws on the marketroid that suggested people should sell Gbe for a corporate backbone and servers with 100 Mb to the workstations. In my case, we typically had 8 48 KB NFS data messages in flight (UDP) or 8 64 KB when using NFS over TCP. 384-512 KB. Oops. (And I used 1 MB TCP window sizes in part to get around an interesting problem with BSD's TCP code sharing a socket across multiple threads and in part to get the "bandwidth x delay" product to get full GbE on a network with a delay as long as 8 msec. I couldn't bring myself to make it bigger.) Given the cost of memory these days, I figured something else must have been behind the atrocious buffering than RAM, and found a big clue in a Cisco document that talked about the FIFOs connecting sections in a GbE switch. Those are basically large, byte at a time shift registers and far more expensive that DRAM. On the smallish switches I had, I couldn't find statistics in the boxes for the number of messages discarded due to congestion. I suspect that may be a marketing solution to what would have been an obvious customer support issue. I never tried buying/borrowing consumer grade switches to abuse, but I'm sure I'd be appalled. Last I looked, implementations of TFTP never let much data on the wire, so that may not be the problem. However, I can imagine a zillion ways something else could screwup. At any rate, without good network traces (at both the 1 GbE and 100 MbE sides), all we can do is speculate where things might be failing. Using a homogenous speed on a network doesn't work well either at times. One NFS client reading from two servers can clog its incoming link just fine. -Ric Werme _______________________________________________ gnhlug-discuss mailing list gnhlug-discuss@mail.gnhlug.org http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss/
