VMFS datastore creation fails on iSCSI LUN newly attached to ESXi host

Products

• VMware vSphere ESXi

Issue/Introduction

• ESXi hosts are newly configured with iSCSI storage.
  
  
• iSCSI vmkernel ports are configured wtih MTU of 9000.
  
  
• The external network path for the iSCSI traffic is configured to support MTU of 9000.
   
• The presented iSCSI devices are detected and have active paths.
  
  
• Creation of a VMFS datastore fails on any of these LUNs with error:
  
  Cannot change the host configuration. Failed to update disk partitions for /vmfs/devices/disks/naa.##########################.
  
   

Environment

VMware vSphere ESXi (all versions)

Cause

Datastore creation fails becausse there is a MTU mismatch between the vmkernel ports used for iSCSI and the vSwitch. Specifically, while the iSCSI vmkernel ports have MTU of 9000, the vSwtich has an MTU of 1500.

Resolution

1. Configure the vSwitch with MTU 9000 to match the vmkernel port configuration.
   
   
2. Confirm end-to-end MTU setting of 9000 by running the following command for each vmk/target IP combination:
   
   vmkping -I <vmkernel_port> -d -s 8972 <target_IP>
   
   
3. Attempt datastore creation again once connectivity is verified.

Additional Information

Troubleshooting ESXi connectivity to iSCSI arrays using software initiators