IBM Storage Systems management command-line interface(Smcli) is a utility that you can use to perform system management tasks from the command line. Here is one of SMcli examples show how to run Read Link Status.
    
Read link status (RLS) error counts refer to link errors that have been detected in the traffic flow of a Fibre Channel loop. The errors detected are represented as a count (32-bit field) of error occurrences that are accumulated over time. The counts provide coarse measure of the integrity of the components and devices on the loop.
    
By analyzing the error counts that are retrieved, you can determine the components or devices within the Fibre Channel loop that might be experiencing problems communicating with the other devices on the loop. A high error count for a particular component or device indicates that it might be experiencing problems and should be given immediate attention.


To Reset the RLS Baseline

SMcli <Ctrl-a-ip> <Ctrl-b-ip> -c "reset storageSubsystem RLSBaseline"   

It resets the RLS baseline counts to 0 for all devices.

To save RLS counts

SMcli <Ctrl-a-ip> <Ctrl-b-ip> -c "save storageSubsystem RLSCounts"   

The baseline describes the error count values for each type of device in the Fibre Channel loop, either when the controller goes through its start-of-day sequence or when you reset the baseline(for case above).
    
The baseline indicates the difference in error counts from the time the baseline was established to the time you request the read link status data.

Note: The same command can run in the SMclient GUI window, chose the storage system --> tool --> execute script, run the command in the command window.

 

RLS Baseline Data for the Storage Subsystem
   

  Type of Data

Description

Devices

A list of all devices on the Fibre Channel loop.

The devices appear in channel order. Within each channel, the devices are sorted according to the device position in the loop.

Baseline time

The date and time when the baseline was set.

Elapsed time

The time that has elapsed from when the baseline time was set to when the read link status was gathered.

Invalid transmission

word (ITW)

The total number of ITW errors that were detected on the Fibre Channel loop from the baseline time to the current  date and time.

ITW might also be referred to as the Received Bad Character Count.

ITW counts indicate that in decoding a read/write transmission, the mapping did not exist and the running disparity of the transmission word is invalid. This data is the key error count to be used when analyzing the error count data.

Link failure (LF)

The total number of LF errors that were detected on the Fibre Channel loop from the baseline time to the current date and time.

 An LF condition is either a link fault signal, a loss of signal, or a loss of ynchronization condition. The LF signal indicates a failure with the media module laser operation.

Loss of synchronization(LOS)

The total number of LOS errors that were detected on the Fibre Channel loop from the baseline time to the current date and time.

LOS errors indicate that the receiver cannot acquire symbol lock with the incoming data stream due to a degraded input signal. If this condition persists, the number of LOS errors increases.

Loss of signal (LOSG)

The total number of LOSG errors that were detected on the Fibre Channel loop from the baseline date to the current date and time.

LOSG errors typically indicate a loss of signal from the transmitting node or the physical component within the Fibre Channel loop. Physical components where a loss of signal typically occurs include the gigabit interface converters(GBICs), the Small Form-factor Pluggable (SFP) transceivers, and the Fibre Channel fiber-optic cable.

     Primitive sequence

            protocol (PSP)

The total number of PSP errors that were detected on the Fibre Channel loop from the baseline date to the current date and time. PSP refers to the number of NPort protocol errors that were detected and Link Reset Response (LRR) primitive sequences that were received while the link is up.

An LRR is issued by another NPort in response to a link reset.

An NPort is a Fibre Channel-defined port at the end of a link, such as a server or a workstation. Each port can act as an originator or a responder (or both) and contains a transmitter and receiver. Each port is given a unique name, called an NPort or an NLPort identifier. If an NPort is connected to a loop, it becomes an NLPort. An NLPort is a Fibre Channel controller ID in a hexadecimal number. The hexadecimal number varies depending on the topology:
     For a private arbitrated loop, the ID is a 1-byte arbitrated loop physical address (ALPA).
     For all other arbitrated loops, it appears as a single 24-bit hexadecimal number (a triplet of domain, area, and ALPA where each field is 1 byte).
     For fabric and point-to-point, the ID is a 3-byte hexadecimal number used in the DID and SID (destination identifier and source identifier) fields of Fibre Channel frames.

          Invalid cyclic

      redundancy check

            (ICRC)

The total number of ICRC errors that were detected on the Fibre Channel loop from the baseline date to the current date and time.

An ICRC count indicates that a frame has been received with an invalid cyclic redundancy check value. A cyclic redundancy check reads the data, calculates the cyclic redundancy check character, and compares the calculated cyclic redundancy check character with a cyclic check character already present in the data. If they are equal, the new data is presumed to be the same as the old data. If the calculated characters and the old characters do not match, an error is posted, and the data is re-sent.

 

Interpreting the RLS Results

The way that you interpret the RLS results is based on the concept that the device immediately following the problematic component will have the largest number of invalid transition word (ITW) error counts. The process is to obtain the ITW count for every component and device on the loop, analyze the data in loop order, and identify any large increases in the ITW counts.