topic Re: Flow Control in Switches, Hubs, and Modems

Flow Control

Paul Hutchings — Fri, 10 Dec 2010 18:43:20 GMT

I have two switches (Procurve 2910al) connected by a 10gbps fiber link on port A1 of each switch.

The switches are for an iSCSI network and the recommendation (HP P4000) is to enable flow control on the SAN NICs and on the switch ports they are connected to.

The 10gbps port is set to carry 2 VLANs tagged, one for iSCSI, the other vMotion.

Do I need flow control enabled on the link port A1?

Secondly, if I do enable it, it's at port level, not VLAN level, does anyone know if it will cause problems with vMotion?

I guess I'm getting a bit muddled about whether it should be enabled only ports linking switches.

Thanks.

Re: Flow Control

Jan-Philipp Warmers — Mon, 13 Dec 2010 08:09:42 GMT

Hello,

First Have you read the Best Practices for HP P4000?

Sometimes iSCSI disallow Switch interconnects.

i would recommend to enable Flow Control on the 10G link.

i vMotion should work better with flow control. because there are no packet drops. Only Pause frames and ESX4.x support that.

Re: Flow Control

Paul Hutchings — Mon, 13 Dec 2010 17:51:59 GMT

Thanks Jan. I have read best practise, which is to enable flow-control, with jumbo frames optional (it suggests you shouldn't need worry about jumbo frames if you have dedicated iSCSI lan until you get to 10gbps or so).

Anyway, I enabled it on all switch ports since these switches are only for iSCSI and vMotion traffic.

Am I right in thinking that you can't globally enable flow control on the 2910al, you have to enable it per port?

Re: Flow Control

Jan-Philipp Warmers — Wed, 15 Dec 2010 09:21:58 GMT

yes, its only on per Port base but you can do

int 1-48
flow-control ....