NFS datastore is inaccessible on all the ESXi

Products

• VMware vCenter Server

Issue/Introduction

Symptoms:

• NFS Datastore went inaccessible after Network Maintenance. 

• NFS The datastore shows 0MB on the vCenter and host UI

• The NFS share cannot be mounted by the ESXi host.

• Error notice on vCenter / Host UI : NFS Error: Unable to connect to NFS server

Validation :

• The below output shows that the VMk2 is configured with MTU 9000.

[root@esxi:~] esxcfg-vmknic -l
Interface  Port Group/DVPort/Opaque Network        IP Family IP Address                              Netmask         Broadcast       MAC Address       MTU     TSO MSS   Enabled Type                NetStack
vmk0       Management Network                      IPv4      ##.##.##.##                           255.255.255.0   ##.##.##.##   ##:##:##:##:##:## 1500    65535     true    STATIC              defaultTcpipStack
vmk1       vMotion                                 IPv4      ##.##.##.##                           255.255.255.0   ##.##.##.##   ##:##:##:##:##:## 9000    65535     true    STATIC              defaultTcpipStack
vmk2       NFS_Adapter                             IPv4      ##.##.##.##                           255.255.255.0   ##.##.##.##   ##:##:##:##:##:## 9000    65535     true    STATIC              defaultTcpipStack

• All packets are dropped when initiating traffic with an MTU of 8972 on the VMK2 interface.

[root@ESXI :~ ] vmkping -I vmk2 -s 8972 <Destination IP>
PING ##.##.##.## (##.##.##.##) : 8972 data bytes
---##.##.##.## ping statistics---
3 packets transmitted, 0 packets received, 100% packet loss

• The traffic works fine over MTU1472 [1500], 

[root@ESXI :~ ] vmkping -I vmk2 <Destination IP>
PING ##.##.##.## (##.##.##.##): 56 data bytes
64 bytes from ##.##.##.##: icmp_seq=0 ttl=64 time=0.158 ms
64 bytes from ##.##.##.##: icmp_seq=1 ttl=64 time=0.213 ms
64 bytes from ##.##.##.##: icmp_seq=2 ttl=64 time=0.167 ms
---##.##.##.## ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 0.158/0.179/0.213 ms

Environment

VMware vSphere ESXi 6.x

VMware vSphere ESXi 7.x

VMware vSphere ESXi 8.x

Cause

• From the above Validation, it is evident that the traffic is working fine over MTU 1500 and not 9000, which indicates the traffic is being dropped over the network path.

Resolution

• Change MTU from 1500 to 9000 on the network switches that are configured between the ESXi and the NFS storage.

Additional Information

Troubleshooting NFS datastore connectivity issues.