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Fibre Channel (SAN)

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Regular Contributor
Posts: 166
Registered: ‎02-05-2014

Re: counters tim_txcrd_z increase

Hmm, I learn new things here all the time or they are absolute nonsense. I preffer to think the latter.

 

First a comment by Eli:

Each frame can "live" in the queue 2.5us, and after this timeout the frame discarded."

 

If that was the case not a single frame would ever reach an HBA or Storage target. 2.5 microseconds is the measuring interval where the ASIC checks on the amount of credits. If it is 0 at that particulate point in time this counter increments by one. The time a frame can live inside a receive buffer is determined by the hold-time which is either 220ms, 500ms or a user defined value.

 

See here on a very nasty trap if you get this wrong: http://erwinvanlonden.net/2013/03/the-emergency-health-threat-eht-on-brocade-fc-fabrics/

 

Secondly:

Buffer credits are defined by the receiving side of a port. That means that during FLOGI and the Accept on that FLOGI the two port tell eachother how much buffers they have/allow the remote side to send without having to obtain an R_RDY primitive.

 

 

See here: http://erwinvanlonden.net/2012/07/one-rotten-apple-spoils-the-bunch-1/

and here http://erwinvanlonden.net/2013/11/buffer-credits-for-newbies/

 

 

Kind regards,
Erwin van Londen
Brocade Distinguished Architect
http://www.erwinvanlonden.net The Fibre Channel blog



Q&A -> https://hackhands.com/elo/


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