Frequent hickups on the networking layer

[Mark Schouten]

Hi,

On 04/29/2015 04:06 PM, Garrett Wollman wrote:

> If you're using one of the drivers that has this problem, then yes,
> keeping your layer-2 MTU/MRU below 4096 will probably cause it to use
> 4k (page-sized) clusters instead, which are perfectly safe.
>
> As a side note, at least on the hardware I have to support, Infiniband
> is limited to 4k MTU -- so I have one "jumbo" network with 4k frames
> (that's bridged to IB) and one with 9k frames (that everything else
> uses).

So I was thinking, a customer of mine runs mostly the same setup, and has no issues at all. The only difference, MTU of 1500 vs MTU of 9000.

I also created a graph in munin, graphing the number of mbuf_jumbo requests and failures. I find that when lots of writes occur to the iscsi-layer, the number of failed requests grow, and so so the number of errors on the ethernet interface. See attached images. My customer is also not suffering from crashing ctld-daemons, which crashes every other minute in my setup.

So tonight I'm going to switch to an MTU of 1500, I'll let you know if that helped.


Regards,

Mark Schouten