Fibre Channel (SAN)

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Occasional Contributor
Posts: 5
Registered: ‎09-13-2010

tim_txcrd_z value increasing steadily

Observed tim_txcrd_z value increasing steadily on the DCX port where a AIX VIO is connected . No other errors obvserved .

What could be cause of this issue ? Any suggestion ?

Valued Contributor
Posts: 761
Registered: ‎06-11-2010

Re: tim_txcrd_z value increasing steadily

Hi,

tim_txcrd_z means that there are no free BB credits to send a frame. Usually this fact, does not mean that there is a problem, unless you start seeing tx_disc_c3 counter increase.

Increasing the number BB credits for that port could help.

Rgds

Frequent Contributor
Posts: 141
Registered: ‎05-26-2009

Re: tim_txcrd_z value increasing steadily

Depending on how quickly (related to the total ticks / related to the sent frames) this counter increases it could point to a slow drain device behavior of your VIOS. And of course you could run into problems way before any frames are dropped. The switch drops frames after 500ms - For all situations where the frames stay in the buffers for <500ms you can still face performance problems without any frame drop. And the back pressure can additionally affect other device pairs as well.

If you notice performance problems (not only for this server but for example also for others using the same ISLs) I recommend to contact the SAN service provicer of your choice and ask them for performance analysis service.

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