This isn't ethernet flow control, this is NFS flow control. Ordinarily, that's two totally different things, HOWEVER there is a link in some cases.
Ethernet flow control is just a mechanism where a receiver can tell a second to cease transmission. We strongly discourage use of ethernet flow control. The problem is ethernet flow control is at the physical layer. If you have a lot of clients attached to one filer and one of those clients gets into trouble and starts sending flow control requests, all transmission on the filer NIC stops. The end result is that your filer is only as fast as your slowest client. The problem is especially exaggerated with gigabit hosts and 10Gb filers. The filer is capable of sending data much faster than a client can receive it, and you can run into lots of flow control activity. Most users will never see a problem, but some will. It's better to disable flow control and let the clients just drop packets. TCP/IP stacks are designed to deal with packet loss.
NFS flow control helps an NFS server project itself from a malfunctioning client. If an NFS client keeps asking for data but never acknowledges receipt, the output TCP buffers on the NFS server would fill up. NFS flow control kicks to stop this. The NFS server will stop transmitting data if there are too many unacknowledged operations.
The message shown below means an NFS client went a full 2 minutes without acknowledging any transmissions. If a NFS client lost power, you're guaranteed to see this message when ONTAP gives up waiting and just clears the remaining data in the buffer.
There are, however, a couple of bugs where ethernet flow control can lead to an NFS flow control glitch which can stall IO. I'd recommend opening a case on this to see if you might be affected.
From: toasters-bounces@teaparty.net [mailto:toasters-bounces@teaparty.net] On Behalf Of tmac Sent: Friday, March 28, 2014 12:52 PM To: Mark Flint Cc: Toasters Subject: Re: NFS fails?
Check Your switch ports Check your NetApp ports
Make SURE that Flow Control is OFF
Check on the Filer: ifstat <port>
On the switch: show int <port>
You should see NONE. If not none, then flowcontrol is on....find a way to get it off.
--tmac
Tim McCarthy Principal Consultant
[Image removed by sender.] [Image removed by sender.] [Image removed by sender.]
Clustered ONTAP Clustered ONTAP NCDA ID: XK7R3GEKC1QQ2LVD RHCE6 110-107-141https://www.redhat.com/wapps/training/certification/verify.html?certNumber=110-107-141&isSearch=False&verify=Verify NCSIE ID: C14QPHE21FR4YWD4 Expires: 08 November 2014 Current until Aug 02, 2016 Expires: 08 November 2014
On Fri, Mar 28, 2014 at 7:22 AM, Mark Flint <mf1@sanger.ac.ukmailto:mf1@sanger.ac.uk> wrote: Hi all, I have an issue with a FAS3170 and NFS. Seems that hosts are being disconnected and the only thing I can find is a strange message that would seem to point at TOE? :-
Tue Mar 4 21:13:49 GMT [netapp5a: nfsd.tcp.close.idle.notify:warning]: Shutting down idle connection to client (172.17.82.34) where transmit side flow control has been enabled. There are 22 outstanding replies queued on the transmit buffer
However, TOE is turned off. If someone could point me in the right direction, it would be much appreciated :)
~Mark
-- The Wellcome Trust Sanger Institute is operated by Genome Research Limited, a charity registered in England with number 1021457 and a company registered in England with number 2742969, whose registered office is 215 Euston Road, London, NW1 2BE.
_______________________________________________ Toasters mailing list Toasters@teaparty.netmailto:Toasters@teaparty.net http://www.teaparty.net/mailman/listinfo/toasters
