Need to report a FICON problem to a System Service Representative, quickly identify a channel path/port to a DASD device or do further problem determination on why a FICON channel path may be experiencing slow performance? The new D M=DEV LINKINFO parameter is for you!
The Read Diagnostic Parameters (RDP) function provided by APAR OA49089 introduces the LINKINFO parameter that offers four ways to display link diagnostic information for a device and channel path identifier (CHPID). The diagnostic information includes the optical transceiver values, error counters, operating and capable speed, and buffer credits for each port in the path.
For switched configurations, information for the channel port, entry switch port, exit switch port, and control unit port is displayed. For point-to-point configurations, information for the channel port and control unit port is displayed. System Service Representatives LOVE the detailed link diagnostic information because it helps them quickly identify the problem area.
OA49089 also adds a new health check (IOS_PORT_SPEED) to check for port speed mismatches for the channel, entry and exit switch, and control unit ports, which can adversely affect performance.
Please note: The RDP function is supported on z/OS V2R1/V2R2 running on z13 GA2(D27I) LPARs for all FICON channels. Contact your switch vendor for information about which switches support RDP and the required firmware level. RDP is supported on the DS8870 Control Unit with the 7.5 level of microcode or DS8880 Control Unit with the 8.1 level of microcode for 16 Gbs host adapter cards only.
This z/OS Read Diagnostics Parameters (RDP) tips document contains the following fast path sections:
New LINKINFO Parameter
LINKINFO Parameter - examples
Examples of how RDP could show additional problems
Message numbers you may want to follow-up on with RDP commands
Documentation/Publications
ROUTE Parameter - Additional helpful command
ROUTE Parameter - examples
New LINKINFO Parameter
The command syntax is D M=DEV,(devno,(chp)),LINKINFO={FIRST|LAST|REFRESH|COMPARE}
- The LINKINFO parameter may only be specified when a path is specified on the D M=DEV command. The examples below show a switched configuration with 16Gb end to end ports. The Buffer Credit and Forward Error Correction (FEC) uncorrected error counters are not available at this time.
- The error counters are cumulative, so seeing a very large error counter may not indicate a problem. Observing how error counters change over time is what matters. Click here for an example.
To quickly access examples of the command results, click on the options in blue.
FIRST - displays the link diagnostic information that was obtained during IPL or when the physical path was brought online for the first time after IPL.
LAST - Displays the link diagnostic information that was last retrieved by the system. The system retrieves new information for a physical path every 24 hours or when LINKINFO=REFRESH is specified.
REFRESH - Requests that the system obtain new link diagnostic information for the physical path and then displays that information. This causes the prior information to be replaced and a subsequent LINKINFO=LAST request will also show this new information.
Note:
1. A REFRESH request does not cause the entry switch port, exit switch port and control unit port to retrieve new optical transceiver information. It simply causes the last retrieved values to be returned to the channel subsystem. The frequency that a port retrieves its own optical transceiver information is manufacturer and model specific.
2. A REFRESH request will be rejected if the channel specified in the command is already processing the maximum number of concurrent requests. These requests could be from this system or other systems on the same processor. The maximum number of concurrent requests allowed for a channel is model dependent.
COMPARE - Displays a comparison of the first and last set of link diagnostic information that was retrieved by the system.
LINKINFO Parameter - examples
FIRST - example: D M=DEV(D800,(94)),LINKINFO=FIRST
- Displays the link diagnostic information that was obtained during IPL or when the path was varied online for the first time after IPL.
LAST - example: D M=DEV(D800,(94)),LINKINFO=LAST
- Displays the link diagnostic information that was last retrieved by the system. The system retrieves new information for a path every 24 hours or when LINKINFO=REFRESH is specified.
REFRESH - example: D M=DEV(D800,(94)),LINKINFO=REFRESH
- Requests that the system obtain new link diagnostic information for the physical path and then displays that information. This causes the prior information to be replaced and a subsequent LINKINFO=LAST request will also show this new information. The error counters are cumulative, so seeing a very large error counter is not necessarily an indication of a problem.
COMPARE - example: D M=DEV(D800,(94)),LINKINFO=COMPARE
- Displays a comparison of the first and last set of link diagnostic information that was retrieved by the system.
Examples of how RDP could show potential problems
How RDP values may look when a fiber optic cable needs cleaning or may be damaged
- The example below uses RDP to monitor an Attenuator test to degrade the optical signal between the Channel and Switch Entry Port. Notice how the Rx Power value changes for the switch Entry Port before and after starting attenuation.
Before
After starting attenuation - Notice the significant drop in Rx power as the Attenuator limits fiber optic light between the Channel and switch Entry Port. This is how it may look when a fiber optic cable needs cleaning or is damaged.
Diagnose Port Speed mismatches that could cause SAN slowness
- The example below shows a port speed mismatch we created for system test. Prior to performing the test, the operating speed for all ports matches the capable speed (16 Gb). During the test, we lowered the switch exit port to operate at a speed of 8 Gb, which is less than the maximum capable speed of 16 Gb. Note the changes to the IOS_PORT_SPEED Health Check and the RDP Refresh command results for Operating Speed and Capable Speed when a port speed mismatch occurs.
Before
IOS_PORT_SPEED Health Check
Notice the Capable Speeds and Operating Speeds are 16G on the Channel and all ports.
After
IOS_PORT_SPEED Health Check
Lowering the switch exit port speed to 8Gb creates an exception.
Notice the Capable Speeds and Operating Speeds for the Exit and Cntl Unit ports are now a mismatch.
Error counters are cumulative. During the attenuator test to degrade the optical signal between the channel and entry switch ports, interface control checks occurred because of the weak optical signal, which resulted in many IOS050I CHANNEL DETECTED ERROR messages. Notice how the error counters (Link Failures, Loss of Signal, Invalid Trans Word and Invalid CRC) changed as a result of the test.
Before
IOS050I CHANNEL DETECTED ERRORs occurring
After
Message numbers that you may want to follow up on with RDP commands
IOS050I CHANNEL DETECTED ERROR ON devno,chp,cmd,stat [,PCHID=pppp] [,EXTSS=ss]
IOS051I INTERFACE TIMEOUT DETECTED ON devno,chp,cmd,stat[,PCHID=pppp][,EXTSS=ss]
IOS054I sdddd,chp ERRORS DETECTED BY component[, component]…
- IOS054I is issued in conjunction with IOS050I and IOS051I and helps to pinpoint which point in the path detected the errors. In this case, it was the channel switch port (entry switch port).
IOS001E devno,INOPERATIVE PATH[S] xx[,chp,chp…]
IOS2001I devno,INOPERATIVE PATHS chp,chp,... STATUS FOR PATH(S) chp,chp,... errortype [errormsg]
IOS002A devno, NO PATHS AVAILABLE STATUS FOR PATH(S) chp,chp,...
IOS071I devn,chp,jobname,text[STATUS:statustext]
Documentation/Publications
1. To exploit the new Read Diagnostic Parameters (RDP) extended link service (ELS) for FICON channels on z13 and z13s processors you'll need APAR OA48089 . Refer to the following URL to see the documentation updates:
http://publibz.boulder.ibm.com/zoslib/pdf/OA49089.pdf
2. z/OS Introduction and Release Guide (GA32-0887) - Introduces the Read Diagnostics Parameters (RDP) functionality provided by APAR OA49089.
3. z/OS MVS System Commands (SA38-0666) - The LINKINFO parameter has been added to the D M=DEV command.
4. z/OS MVS System Management Facility (SA38-0667) - SMF record type 124 has been added.
5. z/OS MVS System Messages Volume 7 (IEB-IEE) (SA38-0674) - RDP display command messages IEE584I and IEE586I have been added.
6. z/OS MVS System Messages Volume 9 (IGF-IWM) (SA38-0676) - Messages IOSHC150I, IOSHC151E, IOSHC152I, IOSHC155I, IOSHC156E and IOSHC157I have been added.
7. IBM Health Checker for z/OS User's Guide (SC23-6843) - The RDP IOS_PORT_SPEED and IOS_BUFFER_CREDITS health checks have been added.
8. Refer to z Systems Planning for Fiber Optic Links (FICON/FCP, Coupling Links, and Open Systems Adapters) GA23-1407-01 for information about the specifications and optical properties for fibre optic links, jumper cables and trunk cables. Refer to System z Maintenance Information for Fiber Optic Links (ESCON, FICON, Coupling Links, and Open System Adapters) SY27-2597-15 for problem determination and cleaning procedures.
Additional helpful command to display routes through Storage Area Networks (SAN)
ROUTE parameter
The D M=DEV command allows you to display the route through the storage area network (SAN) fabric for a specific device and channel path by specifying the ROUTE keyword. Please see the z/OS MVS System Commands (SA38-0666) publication for more information.
The command syntax is D M=DEV(devno,(chp)),ROUTE={TODEV|FROMDEV|BOTH}} {HEALTH}
To see examples of the command results, click the options in blue.
TODEV - Displays the route through the fabric, starting with the channel and going to the device.
FROMDEV - Displays the route through the fabric, starting with the device and going to the channel.
BOTH - Displays the route through the fabric in both directions.
HEALTH - Displays the health information, which includes the utilization, average delay, and error counts, for the fabric, switch, and port. You can add this option to TODEV, FROMDEV and BOTH. Routing and health information will only be determined and displayed when the channel is connected to a switch and the control unit definition for the channel path is defined in the I/O configuration with a two-byte link address.
ROUTE Parameter - examples
TODEV - example: D M=DEV(D800,(9A)),ROUTE=TODEV
- Displays the route through the fabric, starting with the channel and going to the device.
FROMDEV - example: D M=DEV(D800,(9A)),ROUTE=FROMDEV
- Displays displays the route through the fabric, starting with the device and going to the channel.
BOTH - example: D M=DEV(D800,(9A)),ROUTE=BOTH
- Displays the route through the fabric in both directions.
HEALTH - example: D M=DEV(D800,(9A)),ROUTE=TODEV,HEALTH You can add HEALTH to all options(TODEV, FROMDEV and BOTH).
- Displays the health information, which includes the utilization, average delay, and error counts, for the fabric, switch, and port.
