[Beowulf] cheap SMC 8524T gigabit switches, and performance of

[Andrew Piskorski]

FYI, some vendor called Unity Electronics is currently selling a bunch
of 24 port SMC 8524T gigabit switches for c. $120 each on Ebay:

  http://search.ebay.com/search/search.dll?satitle=SMC+gigabit&sass=unityelectronics.com
  http://unityelectronics.com/product-product_id/3942/m/SMC/p/SMC8524T
  http://unityelectronics.com/product-product_id/3941/m/SMC/p/SMC8516T

I haven't actually tried using it yet, but the one I recieved is part
number 751.7398, and appears to be new in box as advertised.

And that reminded me of the interesting thread from April, below, on
performance testing of some (small) SMC gigabit switches:

  http://www.beowulf.org/archive/2007-April/017924.html

On Mon, Apr 02, 2007 at 03:58:06PM -0500, Bruce Allen wrote:
> Subject: Re: [Beowulf] How to Diagnose Cause of Cluster Ethernet Errors?

> Just for kicks have a look at these figures: 
> http://www.lsc-group.phys.uwm.edu/beowulf/nemo/design/SMC_8508T_Performance.html

> Here are some more testing results from different edge switches:
> http://www.lsc-group.phys.uwm.edu/beowulf/nemo/design/switching.html

Bruce, it's interesting how your bandwith tests show the SMC 8508T
721.0154 switch started out with true wire-speed and 9k jumbo frame
performance, 721.8129 was worse, and then 722.8486 was yet worse
again.  Compared to the previous part number, each subsequent revision
of the supposedly "same" SMC8508T model degraded performance!

And your tests were with only 2 of the 8 ports on each switch, so I
wonder how much worse they'd be when using all ports at once.

It's also interesting that all 3 part numbers showed the same
performance for the 2 kb MTU.  The iterative cheapening of the
hardware seems to have only broken the large frame sizes.

However, I'm confused by part of your results:  Some of your crossover
cable and 5 port switch results show a big bandwith advantage when
using jumbo frames - bandwith takes a huge jump up from around 125
MB/s with a 2k MTU to 225 with 4k.  But your 8508T results, on the
other hand, are much better at 2k, around 200 MB/s, and then gradually
moves up to about the same 225 at 4k.  Any idea why you saw those
different behaviors?

-- 
Andrew Piskorski <atp at piskorski.com>
http://www.piskorski.com/