Learn About Read Link Status Diagnostics

A  loop is an interconnection  used to connect  components and storage arrays. The storage management software uses the connection between the  machine and each  in the storage array to communicate with each component and storage array on the loop.

During communication between storage arrays,  are detected within the traffic flow of the loop. Error count information is accumulated over a period of time for every component and storage array, including:

Error counts are calculated from a , which describes the error count values for each type of storage array in the Fibre Channel loop. Calculation occurs from the time when the baseline was established to the time at which the error count information is requested.

The baseline is automatically set by the RAID controller module. However, a new baseline might be set manually through the Read Link Status Diagnostics dialog. For more information, see Running the Read Link Status Diagnostic.

Analyzing Read Link Status Results

Analysis of the RLS error count data is based on the principle that the storage array immediately "downstream" of the problematic component should see the largest number of error counts.

Important: Because the current error counting standard is vague about when the  count is calculated, different vendors' storage arrays calculate errors at different rates. Analysis of the data must take this into account.

The analysis process involves obtaining an ITW error count for every component and storage array on the loop, viewing the data in loop order, and then identifying any large jumps in the ITW error counts. The following graphic shows the typical error count information displayed in the Read Link Status Diagnostics dialog.

In addition to the ITW count, the following error counts are displayed in the Read Link Status Diagnostics dialog.

Error Count Type

Definition of Error

Link Failure (LF)

When detected,  indicate that there has been a failure within the media module laser operation.

Link failures might also be caused by a link fault signal, a loss of signal, or a loss of synchronization.

Loss of Synchronization (LOS)

Indicates 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 Loss of Signal errors increases.

Loss of Signal (LOSG)

Indicates a loss of signal from the transmitting node or physical component within the Fibre Channel loop.

Physical components where a loss of signal typically occurs include the gigabit interface connectors, and the Fibre Channel fiber-optic cable.

Primitive Sequence Protocol (PSP)

Refers to the number of  protocol errors detected, and Link Reset Response (LRR) primitive sequences received while the link is up.

A Link Reset Response (LRR) is issued by another N_Port in response to a link reset.

Invalid Cyclic Consistency Check (ICRC)

Indicates that a frame has been received with an  value.

A cyclic consistency check is performed by reading the data, calculating the cyclic consistency check character, and then comparing its value to the 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.

Note: When analyzing RLS data for a storage array that contains both SATA physical disks and a RAID controller module in a single enclosure, you will see NA (Not Applicable) for each SATA physical disk in this enclosure. This is because the SATA physical disks are not communicating with the RAID controller module via the Fibre Channel (FC) protocol. However, if there are any SATA expansion expansion enclosures in the array, the EMMs in those enclosures are identified as Fibre Channel devices and will report meaningful RLS data back to the RAID controller module. The SATA physical disks behind the EMMs will report RLS data, but this data will be coming from the Fibre-to-SATA translation circuitry in the EMM.

If you are unable to determine which component or storage array on your Fibre Channel loop is experiencing problems, save the RLS Diagnostics results, and forward them to Customer and Technical Support for assistance.

Related Topics

Running the Read Link Status Diagnostics