seb_ 060000QVK2 Visits (4855)
From time to time (sometimes everyday - the support business is a capricious one) I need to see what's really going on in the fibre. For that reason we have a couple of tracers which can be sent to the EMEA countries. Some IBM organizations in some countries even have their own tracers. For the SAN support we use the XGIGs from JDSU (originally from Finisar). Usually I trace, if the problem is somehow protocol related and cannot solved with the RAS packages of the switches and the devices. Or if the RAS information from one device contradicts the other one. Or if every support team (internal and external) points to each other. Or if something totally strange happens and nobody can deal with it. Maybe we trace a little too often, because meanwhile other vendors sometimes say things like "Oh, you also have IBM gear in your environment? Let them trace it!".
So what's this tracing all about?
To put it simple, you connect it in the line and it just records all the traffic. Of course you can filter it and let it trace only the interesting part of the frames. I do not care for the actual data but the FCP and the SCSI header info are precious information. Of course an 8 Gbps link generates a lot of data, too and the memory is very limited. So you want to be sure to trace exactly what you need - not more, not less. The tracing is done by IBM customer engineers. We ensure to have a suitable number of trained CEs in every region. I hosted some of the trainings by myself and imho it's definitely worth it. The analysis is then done afterwards. I personally like it, because it offers me a possibility to not be "bound" to the RAS packages alone. I can really see what happens.
Although the whole topic is pretty much straight forward, for the ones unfamiliar with it, tracers seem to be mystical devices. Over time I faced several "urban legends" impeding troubleshooting a lot sometimes:
These were just some of the rumors and statements I heard in the past. To summarize it, please keep in mind:
A tracer is not a magical device. It just records traffic.