Path redundancy to the storage device is degraded (1009555)

Details

You are experiencing these issues:

• ESX host has lost a redundant path to a storage device and there are still more than one active paths left
• The Task and Events tab of the ESX host on the vSphere Client reports the error:
  
  Path redundancy to storage device DeviceName degraded. Path vmhbaN:Cx:Ty:Lz is down. Affected datastores: DatastoreName
• ESX host and virtual machines continue to access the storage device through the remaining active paths

Solution

If vmhba3:C0:T1:L7, which is one of the many active paths to a specified storage device, goes down, you see the message:

Path redundancy to storage device naa.60a9800043346534645a433967325334 degraded. Path vmhba3:C0:T1:L7 is down. Affected datastores: Datastore1

The situation indicates a single point of failure and poses a performance impact in the virtual machines currently accessing the storage device.

The storage device reading vmhba3:C0:T1:L7 in the example contains several potential failure points:

• vmhba35 - HBA (Host Bus Adapter)
• C1 - Channel
• T0 - Target (Storage processor port)
• L7 -  LUN (Logical Unit Number or Disk Unit)

To determine the actual failure or to eliminate possible issues:

1. Identify the available storage paths to the reported storage device by running the esxcfg-mpath -l command. For more information, see Obtaining LUN pathing information for ESX hosts (1003973).
2. Check that a rescan does not restore visibility to the targets. Follow the steps in Performing a rescan of the storage (1003988) to rescan the storage device by using the command-line interface and VMware vSphere Client.
3. Determine whether the connectivity issue is with the iSCSI storage or the fiber storage. Perform one of these options depending on what your connectivity issue is:
   • To troubleshoot the connectivity to the iSCSI storage using the software initiator:
   • 1. Check whether a ping to the storage array fails from ESX. For more information, see Testing network connectivity with the ping command (1003486).
     2. Check whether a vmkping to each network portal of the storage array fails. For more information, see Testing VMkernel network connectivity with the vmkping command (1003728).
     3. Check that the initiator is registered on the array. Contact your storage vendor for instructions on this procedure.
     4. Make sure that this physical hardware is correctly functioning:
     5. • Ethernet switch
        • Ethernet cables between the switch and the ESX host
        • Ethernet cables between the switch and the storage array
           
   • To troubleshoot the connectivity to the fiber attached storage, ensure that:
     • The fiber switch zoning configuration permits the ESX host to see the storage array. Consult your switch vendor if you require assistance.
     • The fiber switch propagates RSCN messages to the ESX hosts. To configure the fiber switch, see Configuring fibre switch so that ESX Server doesn't require a reboot after a zone set change (1002301).
4. Check the physical hardware, including:
   • The storage processors on the array
   • The fiber switch and the Gigabit Interface Converter (GBIC) units in the switch
   • The fiber cables between the fiber switch and the array
   • The array itself

Important: A rescan is required after any change is made to see if the targets are detected.

Source:-

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1009555