Flow Control Question

par4-eric · ‎02-26-2010

Hi,

I am setting up Flow control on my switches for our SAN environment. What is the best configuration for this should it be set to Tx, Rx or both on the switch?

Thank you in advance.

Ganesh Hariharan · ‎02-26-2010

Hi,
I
am setting up Flow control on my switches for our SAN environment. What
is the best configuration for this should it be set to Tx, Rx or both on the switch?
Thank you in advance.

Hi ,

Flow control prevents the attached devices from being overcongested by the datatraffic. When the receiving station buffer becomes full switch holds the frame sent to the switch and once buffer of the station becomes free it requeues the traffic and check out the following things before implemeting flow control on switches:-

When configuring flow control, note the following information:

Because auto negotiation does not work on 10 Gigbit Ethernet fiber optic ports, they respond to pause frames by default. On 10 Gigbit Ethernet fiber optic ports, the flow-control operational mode is always the same as administrative mode.

You cannot configure how WS-X6502-10GE 10-Gigabit Ethernet ports respond to pause frames. WS-X6502-10GE 10-Gigabit Ethernet ports are permanently configured to respond to pause frames.

When configuring how a port responds to pause frames, note the following information:

For a Gigabit Ethernet port, when the configuration of a remote port is unknown, you can use the receive desired keywords to configure the Gigabit Ethernet port to respond to received pause frames. (Supported only on Gigabit Ethernet ports.)

Use the receive on keywords to configure a port to respond to received pause frames.

Use the receive off keywords to configure a port to ignore received pause frames.

When configuring transmission of pause frames on a port, note the following information:

For a Gigabit Ethernet port, when the configuration of the remote ports is unknown, you can use the send desired keywords to configure the Gigabit Ethernet port to send pause frames. (Supported only on Gigabit Ethernet ports.)

Use the send on keywords to configure a port to send pause frames.

Use the send off keywords to configure a port not to send pause frames.

Hope to Help !!

Ganesh.H

par4-eric · ‎02-26-2010

Thanks for the response. I am not very technical when it comes to networking or switches so this didn't exactly answer my question. I just need to know the best practice when configuring a SAN environment pertaining to flow control should it be set to Tx on/off, Rx on/off or both on?

Thanks.

Ganesh Hariharan · ‎02-26-2010

Thanks for the response. I am not very technical when it comes to networking or switches so this didn't exactly answer my question. I just need to know the best practice when configuring a SAN environment pertaining to flow control should it be set to Tx on/off, Rx on/off or both on?

Thanks.

OK as the defination for flow control says that it is a feature that Gigabit Ethernet ports use to inhibit the transmission of incoming packets. If a buffer on a Gigabit Ethernet port runs out of space, the port transmits a special packet that requests remote ports to delay sending packets for a period of time. This special packet is called a pause frame.

And as your environemnt is SAN where huge amount of data will be shared between switches so i would suggests you to configure both.

Hope to Help

Ganesh.H

gpalafoxacs · ‎03-04-2010

Hello,

Equalogic suggest both send and receive, this is if you are using iSCSI, in my experience I follow this recommendation no matter will be the SAN.

Hope this help.

GPS.