Fibre Channel (SAN)

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Contributor
Posts: 21
Registered: ‎04-08-2016

Trying to understand Virtual Channel

[ Edited ]

In one of my DCX  i could see the value of " tim_txcrd_z " in portstatsshow is getting increased for few ports, which are N8gbps with autonegotiation enabled.

 

All these ports are connected to the FC port of the storage  ( 4 node SVC ).

 

Each WWPN has nearly 85 zonemembers.

 

 

Contributor
Posts: 66
Registered: ‎12-24-2015

Re: tim_txcrd_z, value getting increased

Hi!

Change the fillword on port with this increasing counter to value=3.

Be careful, for traffic throught this port operation will be distruptive.

Contributor
Posts: 21
Registered: ‎04-08-2016

Re: tim_txcrd_z, value getting increased

Thanks for the input. Let me try.


pavel.v.minyaev wrote:

Hi!

Change the fillword on port with this increasing counter to value=3.

Be careful, for traffic throught this port operation will be distruptive.


 

Brocade Moderator
Posts: 105
Registered: ‎04-27-2009

Re: tim_txcrd_z, value getting increased

Hi,

 

the fillword setting should have no affect on this counter increasing.

 

it is normal that tim_txcrd_z is increasing on ports, this is not necessarily an issue. There are several factors that contribute to this counter increasing faster for some ports. The rule of thumb is to look at the ratio between stat_ftx (frames transmitted) and this tim_txcrd_z. If the ratio is low, lets say below 30% it should be no issue.

 

The counter increments at 2.5 microsecs ticks if there is no tx credit available and a frame is waiting in the queue to be sent out. However this does not mean that there are too less credits on that port, its more that the attached device is not returning R_RDYs fast enough. And there are also many contributors to this. e.g oversubscription, etc... Always think of this counter of an indicator, not an error. 

If this provided you with a solution to this issue, please mark it with the button at the bottom "Accept as solution".

Any and all information provided by me is not reviewed, approved or endorsed by Brocade and is provided solely as a convenience for Brocade customers. All systems and all networks are different and unique. If you have a service affecting network problem, please open a TAC service request for service through Brocade, or through your OEM equipment provider.
Contributor
Posts: 21
Registered: ‎04-08-2016

Trying to understand Virtual Channel

[ Edited ]

Thomas.Letsche wrote:

Hi,

 

the fillword setting should have no affect on this counter increasing.

 

it is normal that tim_txcrd_z is increasing on ports, this is not necessarily an issue. There are several factors that contribute to this counter increasing faster for some ports. The rule of thumb is to look at the ratio between stat_ftx (frames transmitted) and this tim_txcrd_z. If the ratio is low, lets say below 30% it should be no issue.

 

The counter increments at 2.5 microsecs ticks if there is no tx credit available and a frame is waiting in the queue to be sent out. However this does not mean that there are too less credits on that port, its more that the attached device is not returning R_RDYs fast enough. And there are also many contributors to this. e.g oversubscription, etc... Always think of this counter of an indicator, not an error. 




Thanks a lot for your update on this.

 

yes it is something related to VC, i could see VC2 is getting overloaded in this case.

tim_txcrd_z             628         Time TX Credit Zero (2.5Us ticks)
tim_txcrd_z_vc  0- 3:  0           0           628         0

 

I am trying to understand the VC concept competely from the basic, can someone please help me in getting the complete guide to Virtual Channel.

 

Is there any command to check the over utilized VC and under utilized VC in director DCX?

 

Brocade Moderator
Posts: 414
Registered: ‎03-29-2011

Re: Trying to understand Virtual Channel

Hi,

 

The Admin Guide a few details - best coverage is really in the TS300 troubleshooting course

 

http://www.brocade.com/content/html/en/administration-guide/fos-740-admin/GUID-F758381D-0929-4C23-8EB4-EE3C93F06BA0.html

 

there a few old post which in the community available - brief

 

https://community.brocade.com/t5/Fibre-Channel-SAN/ISL-and-virtual-channels/m-p/71604

 

Longer and more details

 

http://community.brocade.com/t5/Fibre-Channel-SAN/How-are-BB-Credits-Allocated-to-Virtual-Channels/td-p/35087

 

From Sebastian Thäle san blog - he has more about VC in his blogs

 

https://www.ibm.com/developerworks/community/blogs/sanblog/entry/how_to_not_connect_an_svc_in_a_core_edge_brocade_fabric16?lang=en

 

 




If this provided you with a solution to this issue, please mark it with the button at the bottom "Accept as solution".


Any and all information provided by me is not reviewed, approved or endorsed by Brocade and is provided solely as a convenience for Brocade customers. All systems and all networks are different and unique. If you have a service affecting network problem, please open a TAC service request for service through Brocade, or through your OEM equipment provider. If this provided you with a solution to this issue, please mark it with the button at the bottom "Accept as solution"
Contributor
Posts: 21
Registered: ‎04-08-2016

Re: Trying to understand Virtual Channel

Great, thanks for the information. Hope this will help me. Thanks a lot for your time as well.

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