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Troubleshooting iSCSI LUN connectivity issues on ESX/ESXi hosts (1003681)

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  • No targets from an array are seen by:

    • All of the ESXi/ESX hosts
    • All of the ESXi/ESX hosts on a specific switch or connected through an uplink
    • One ESXi/ESX host

  • Targets on the array are visible but one or more LUNs are not visible
  • An iSCSI LUN not visible
  • An iSCSI LUN cannot connect
  • There are connectivity issues to the storage array
  • A LUN is missing
  • In all the cases the device does not show up under iSCSI Storage Adapter


To resolve this issue, validate that each troubleshooting step below is true for your environment. Each step provides instructions or a link to a document, in order to eliminate possible causes and take corrective action as necessary. The steps are ordered in the most appropriate sequence to isolate the issue and identify the proper resolution.

  • The troubleshooting steps outlined in this article apply for both software iSCSI and hardware dependent iSCSI configurations as all network connections between the host and iSCSI array are maintained by the ESXi/ESX network stack.
  • For hardware independent iSCSI HBAs, troubleshooting is done from the BIOS of the HBA or from a vendor-supplied management tool. The HBA itself maintains the network connection and there are minimal troubleshooting options that can be performed from the ESXi/ESX console for these HBAs. VMware may recommend configuring a software iSCSI interface on a host to aid in troubleshooting iSCSI array connectivity issues with hardware independent iSCSI configurations.

The steps outlined below may involve terminal commands. Depending on the version of ESXi/ESX used, the procedure for running terminal commands vary:

To troubleshoot VMware ESXi/ESX to iSCSI array connectivity:

Note: This rescan is required after every storage presentation change to the environment.

  1. Log in to the ESXi/ESX host and verify that the VMkernel interface (vmk) on the host can vmkping the iSCSI targets by running this command:

    # vmkping target_ip

    If you are running an ESX host, also check that Service Console interface (vswif) on the host can ping the iSCSI target by running this commadn:

    # ping target_ip

    Note: Pinging the storage array only applies when using the Software iSCSI initiator. In ESXi, ping and ping6 both run vmkping. For more information about vmkping, see Testing VMkernel network connectivity with the vmkping command (1003728).

  2. Run this netcat (nc) command to verify that you can reach the iSCSI TCP port (default 3260) on the storage array from the host:

    # nc -z target_ip 3260

    Example output:

    Connection to 3260 port [tcp/http] succeeded!

    Note: The netcat command is available with ESX 4.x and ESXi 4.1 and later.

  3. Verify that the host Hardware Bus Adapters (HBAs) are able to access the shared storage. For more information, see Obtaining LUN pathing information for ESX or ESXi hosts (1003973).
  4. Confirm that no firewall is interfering with iSCSI traffic. For details on the ports and firewall requirements for iSCSI, see Port and firewall requirements for NFS and SW iSCSI traffic (1021626). For more information, see Troubleshooting network connection issues caused by firewall configuration (1007911).

    Note: Check the SAN and switch configuration, especially if you are using jumbo frames (supported from ESX 4.x). To test the ping to a storage array with jumbo frames from an ESXi/ESX host, run this command:

    # vmkping -s MTUSIZE IPADDRESS_OF_SAN -d

    Where MTUSIZE is 9000 - (a header of) 28, which is 8972, and the -d option indicates "do not fragment".

  5. Ensure that the LUNs are presented to the ESXi/ESX hosts. On the array side, ensure that the LUN IQNs and access control list (ACL) allow the ESXi/ESX host HBAs to access the array targets. For more information, see Troubleshooting LUN connectivity issues on ESXi/ESX hosts (1003955). Also ensure that the iSCSI name of the iSCSI software adapter is consistent with the storage array.

    Additionally ensure that the HOST ID on the array for the LUN (on ESX it shows up under LUN ID) is less than 255 for the LUN. The maximum LUN ID is 255. Any LUN that has a HOST ID greater than 255 may not show as available under Storage Adapters, though on the array they may reside in the same storage group as the other LUNS that have host IDs less than 255. This limitation exists in all versions of ESXi/ESX from ESX 2.x to ESXi 5.x. This information can be found in the maximums guide for the particular version of ESXi/ESX having the issue.

  6. Verify that a rescan of the HBAs displays presented LUNs in the Storage Adapters view of an ESXi/ESX host. For more information, see Performing a rescan of the storage on an ESXi/ESX host (1003988).
  7. Verify your CHAP authentication. If CHAP is configured on the array, ensure that the authentication settings for the ESXi/ESX hosts are the same as the settings on the array. For more information, see Checking CHAP authentication on the ESXi/ESX host (1004029).
  8. Consider pinging any ESXi/ESX host iSCSI initiator (HBA) from the array's targets. This is done from the iSCSI host.
  9. Verify that the storage array is listed on the Storage/SAN Compatibility Guide. For more information, see Confirming ESXi/ESX host hardware (System, Storage, and I/O) compatibility (1003916).

    Note: Some array vendors have a minimum-recommended microcode/firmware version to operate with VMware ESXi/ESX. This information can be obtained from the array vendor and the VMware Hardware Compatibility Guide.

  10. Verify that the physical hardware is functioning correctly, including:

    • The Storage Processors (sometimes known as heads) on the array
    • The storage array itself
    • Check the SAN and switch configuration, especially if you are using jumbo frames (supported from ESX 4.x). To test the ping to a storage array with jumbo frames from ESXi/ESX, run this command:


      Where MTUSIZE is 9000 - (a header of) 28, which is 8972, and the -d option indicates "do not fragment".

    Note: Consult your storage array vendor if you require assistance.

  11. Perform some form of network packet tracing and analysis, if required. For more information, see:

Note: If your problem still exists after trying the steps in this article:

Additional Information


iscsi-connectivity iscsi-hardware-software-initiator esx-esxi-iscsi-connectivity

See Also

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