Data Domain: SAS Cable Configuration, Topology checks, and Testing

SAS Cable Configuration and Testing
If a SAS cable is faulty, the system can experience sluggishness which can lead to the following error conditions in the Autosupport and its alerting mechanism.

PURPOSE:
This article lists steps on how to ensure that:

• Serial Attached SCSI (SAS) cables are configured using the correct topology and that
• The cable connectors are securely fastened and support the necessary data throughput
• Ensure Correct Topology for Storage Configuration
• Ensure that Connectors are Securely Fastened
• Testing Cable Connections and Data Throughput

• Data Domain systems with External Storage 
• All Software Releases

If a SAS cable is faulty, the system can experience sluggishness which can lead to and report the following error conditions in the Autosupport (ASUP) and its alerting mechanism:

• Enclosure multipath path fails back to single path
• Alert: Duplicate WWN 50050cc1011820cf found in 3.B.?, Loop back to HBA port 4a
• Encl <enclosure id> (<enclosure serial #>) Disk <disk id> only has one active connection path and the required number is 2
• Disk <disk id> is absent and should be replaced
• Disk <disk id> is failed and should be replaced
• Disk <disk id> is unknown and should be replaced
• In an enclosure, multiple disks can be seen in an absent, failed, unknown state, or even a known state
• "se enclosure show detailed-status 2" displays "Host or EXP N port link speed <12.0 Gbps on ES20" OR "<24 Gbps" on an ES30 or DS60
• "se enclosure show detailed-status 2" displays "Host or EXP N port link speed 0 .0 Gbps (disconnected)"
• Faulty Link Displays 9.0 Gbps (that is <12.0 Gbps on ES20 OR <24 Gbps on ES30/DS60)

1. Verify that a SAS cable is connected and working properly.

At the Command Prompt type:

enclosure show topology

Confirm primary and secondary paths to each enclosure to be good without any question marks:


A defective SAS cable shows question marks (???) between paths and the error message stating a problem has been detected:

Port      enc.ctrl.port        enc.ctrl.port       enc.ctrl.port
3a    >   5.A.H:5.A.E   ? ? ?  7.B.H:7.B.E    >    6.B.H:6.B.E 

Error message: ? - A possible problem was detected for this shelf controller or the cable connected to it.

2. If question marks (?) are seen between paths, physically inspect the SAS cable connectivity between shelves. If all cables are snug and securely fastened, however, the alert has not cleared, further troubleshooting is required. Contact Dell Support and Create a service request.
3. If exclamation marks (!) are seen between paths, it indicates that a PHY error has been recorded. Contact Dell Support for help with running diagnostics:

Port      enc.ctrl.port        enc.ctrl.port       enc.ctrl.port
3a    >   5.A.H:5.A.E     !    7.B.H:7.B.E     >   6.B.H:6.B.E  

4. Causes of a Duplicate WWN alert:

• Loose or defective cables
• Connecting an Expansion Port directly to the HBA (SAS Card) port (for example 6.B.E > 4a)
• Incorrect connections between enclosures in the daisy chain

Check all connections and verify that the cabling is in the Data Domain best practices guide. 
A reboot may be required to reset the chain once fixed.
Below is an example of a single DS60 shelf connection with the expected connection speeds:

se enclosure show detailed-status 2 

Encl 2
         Model                   DS60
         Capacity                60 Slots
         WWN                     N/A
         Serial #                xxxxxxxxxx0056
         Number of Controllers   2

         Controller A
                        WWN        500604811017B07F
                        Firmware   2.10.1
                        Serial #   xxxxxxxxxx0162
                        Status     OK

         Expander   Device       Speed       Description
        ---------   ----------   ---------   -------------------------
                    HOST port    24.0 Gbps  <<< Expected connection speed 
                    EXP'N port   0.0 Gbps   <<< 0.0 Gbps will be displayed if there is no physical cable connected

• Data Domain: Troubleshooting Adding a Shelf | Additional Storage | Enclosure (Log in as a registered Dell Support user may be required to view this article.)
• Data Domain ES30 Expansion Shelf Hardware Guide (Log in as a registered Dell Support user may be required to view this document.)
• Data Domain ES30 Expansion Shelf and FS15 SSD Shelf Hardware Guide
• Data Domain DS60 Shelf Expansion Hardware Guide