Flow Control

if your switch supports it just enable it

I think the fact that it's off by default on the Celerra side has more historical reasons

Right - it's disabled by default primarily for historical reasons (it was disabled in the past, and this has never been changed), not because it shouldn't be used.  Rules for enabling flow control would be the same for Celerra as nearly any other host.

Like Gustavo says, Ethernet flow control has very limited capability (will only help in cases where the switch is unable to process traffic as quickly as it's receiving it (most common on switches with oversubscribed blades) or of the Celerra can't process the frames from the NIC quickly enough.  This second situation is incredibly rare).  But there's very little reason NOT to enable it in both directions.

Do you have any recommendations or best practices to follow on enabling flow control on the Celerra for tx only, rx only, or full (both tx and rx)?  The generic recommendation I was looking to follow speaks to enabling tx flow control only for iSCSI, yet when I look at the default configuration of a comparable multiprotocol NetApp filer, flow control is enabled as full (both tx and rx).

Thank you,

Jas

Hi,

I only enable it when I face this type of situation where the switch is congested ( buffer overflow ). On this cases, I use to enable it on both directions.

There should be no problem in enabling it on both tx and rx.

Remember it would only come into play on peak times when the switch is unable to handle the I/O.

Gustavo Barreto.

Thanks for your help and comments.  I decided to write blog post braindumping my thoughts.

http://www.boche.net/blog/index.php/2010/11/29/flow-control/