Cisco switches are what is called store-and-forward. This requires a different technique depending on the brand of switch.
Secondly the way that they check and forward frames is different. Why Does It Matter What Brand Of Switch It Is?įirst, the different brands of switches use different commands to obtain the data you need to troubleshoot these problems. 90 or so seconds later, the application would time out and initiate recovery for a problem that should never have happened. They also had an adapter in the host with a bug in it, and it would simply sit and wait for the storage to respond. When the storage received a bad frame, it simply dropped it and did not send an ABTS. Many of the links were questionable and producing CRC errors. They had over-redundancy (there is such a thing) on the switches and links between the hosts and the storage. Years ago I had customer that was experiencing extremely long delays on their Brocade fabric. A customer I have been working with for the last several months was in this situation and is finally finishing a very long process of cleaning up many faulty links. Also, you will go from 1 or 2 bad links to many. Left unchecked the problem will get worse and eventually cause performance problems. Why Does Fixing These Matter?Īt best, the effect of faulty links is a few dropped frames. What the receiver does with the damaged frame depends on whether it's a switch or end device and if it is a switch, what brand of switch. Troubleshooting that will be a separate blog post, some day. It is much less common, but still possible to have a bad component in the switch. The only time these happen is if the physical plant - cabling, SFPs is somehow defective. If the receiver gets a different answer then what's recorded in the frame, then the frame was changed in flight. When the receiver gets the frame, the receiver repeats the math. The more complicated answer is that before a fibre-channel frame is sent, some math is done. The simple answer is that CRC errors are damaged frames. Having said that, before we can fix them, we need to know what CRC errors are and why they occur. It can be, but usually takes multiple steps. I frequently have customers who want it to be a one step process. You make a change, you monitor your fabric, and if necessary you make more changes until the issues are resolved. Troubleshooting CRC Errors On Storage Networksīefore I say anything else, I will say that there is no "Easy Button" for troubleshooting CRC errors.
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