Category Archives: Fibre Channel

FPIN – The Holy Grail of SAN Stability

As some of you may recall about a decade ago I made a proposal to incorporate more intelligence into the end-devices to be able to better react to changing conditions in fabrics. I called it the “Error Reporting with Integrated Notification” framework (mind the acronym here. :-))

Basically the intention was to have end-devices check for errors along paths which their frames traverse by sending a “query-frame” to the remote device. Each hop along the way could then add its values (errors, counters) to that frame and the remote device would, upon reception of that frame, also add its counters, reverse the SID (Source ID) and DID (Destination ID) and send that same frame back to the original sender. That sender would then be able to make decisions whether to use that same path for subsequent frames or if it would hold of using it temporarily or not at all. Read on.

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Initiator, Target, Both or None ??

Whenever you’ve encountered an output of a nameserver entry you may have come across the phenomenon that the fabric has no clue what the attached device is. For a FC switch an attached device (or N-port in technical terms) is not more than a source or destination where frames originate from or can be sent to. As soon as smarter functions are required it may be helpful (or required) to be able to obtain more information from that device.

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Data Corruption in Storage Area Networks

If there is one thing that gets people relatively annoyed is that their data is not available for a certain amount of time. You can’t get to your sales data, orders cannot be fulfilled, your tracking and tracing options for your goods on their way to your customers does not show up etc. That makes you really crunching your teeth whilst waiting for this stuff to come back. Take that feeling into your head and extrapolate it to the point you start to realize this will not return, ever…….got it? That is when data-corruption has made its mark.

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Why FDMI is compulsory (or should be!!)

FDMI stands for Fabric Device Management Interface and is such an enormously cool feature and unfortunately one of the least used. From an operational management perspective FDMI provides a wealth of information to the fabric regarding the attached devices. The thing that flabbergasted me is that almost no device (HBA/Array) has this turned on of even has the functionality embedded.

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Port stuck in L-port mode

So now and then you run into this issue where, no matter which configuration you try, a switch port always shows:

  86   10    6   3a5600   id    N8       Online      FC  L-Port  1 public

Even though all settings seem to be OK, fillwords are correct, HBA or array settings are the same as others, no port-errors are seen from a switch perspective but this port will not come up as an F-port.

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Signal quality and link stability

I really think I should stop with fillword discussions but here is one more. What happens even if you have set the correct fillword, have made sure all hardware is in tip-top shape and still the encoding errors fly around like a swarm of hornets. Then the problem of ISI might be more problematic.

The main issue still is that the receiving side is unable to distinguish between a 0 and 1. The so called eye-pattern is too narrow or too distorted in such a way the receiver is just seeing gibberish.

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