Our SAN consists of some Brocade 5100 FC-switches, three storage systems and a number of servers. The none of the switches are inter-connected (no inter-switch links). All servers, switches and storage systems are located within the same server room.
I have started looking closer at some counters in our FC switches. On of them, SW-MIB::swFCPortNoTxCredits, counts
the number of times when the transmit credit has reached zero
(qouting from the MIB)
I have a hard time finding descriptions of the concept of transmit credits. But from the little that I've found, it seems to be used for some kind of FC congestion control, and it seems to be particularly interesting on SANs with long-distance fibers.
One of the ports is connected to an IBM XIV storage system. The storage system is believed to be busy, but not over-loaded. However, we do suspect that this storage system sometimes has some latency issues. I see no swFCPortRxCrcs, swFCPortRxBadOs or swFCPortRxEncOutFrs for the port.
My question: What numbers or patterns for swFCPortNoTxCredits would constitute a problem?