Unable to mount existing iSCSI datastore on newly added ESXi host

Products

• VMware vSphere ESXi

Issue/Introduction

Symptoms:

• Existing iSCSI datastore does not mount on newly added ESXi host in vSphere Cluster.
  
  
• Datastores are already mounted on the existing hosts.
  
  
• Presenting of the existing LUNs of these datastores to this new host is correctly configured.
  Devices are detected on the host under 'Storage devices' section of vSphere Client.
  
  
• vobd logs in newly added ESXi reports following:
  
  2025-05-21T14:19:01.528Z In (14) vobd[2097763]: [iscsiCorrelator] 6212462175998 us: [vob. iscsi. discovery. connect. error] discovery failure on vmhba64 to #.#.#.# because of a network connection failure. 

2025-05-21T14:19:01.529Z In (14) vobd[2097763]: [iscsiCorrelator] 6212462175741 us: [esx.problem. storage. iscsi. discovery. connect. error] iSCSI discovery to #.#.#.# on vmhba64 failed. The iSCSI Initiator could not establish a network connection to the discovery address.

Environment

vSphere ESXi 7.x 

vSphere ESXi 8.x

Cause

• Jumbo frames configuration used for iSCSI traffic is to consistent end to end.
  
  
• Virtual switch and vmkernel adapter for iSCSI both were configured with MTU of 9000 but network switch connected to the ESXi hosts had its port configured with MTU value lower than 9000.

Resolution

1. Change the MTU value to 9000 on network switch port to establish iSCSI connection on new host.
   
   
2. Run 'Rescan storage' on new ESXi host in vSphere Client to allow mounting of the iSCSi datastores.