Was setting up a NFS volume in openfiler for a lab and hit this strange error on the ESXi host:

2014-09-25T18:36:53.522Z cpu11:32806)WARNING: NFS: 316: Lost connection to the server mount point /mnt/data01/vol01/Openfiler01/, mounted as 05730b90-cf23e830-0000-000000000000 ("Openfiler01")  
2014-09-25T18:36:54.524Z cpu10:216948)WARNING: NFS: 2144: Failed to get attributes (I/O error)  
2014-09-25T18:36:54.524Z cpu10:216948)NFS: 2207: Failed to get object 36 5730b90 cf23e830 70001 8000080 0 dc16020f c9496472 871a149a 2fb062cb 0 0 0 :I/O error  

On the ESXi host, i was able to mount the volume successfully and everytime i tried accessing files on the volume, it would go inactive and I had to remove and mount the nfs volume again.

To remove the nfs datastore:

esxcli storage nfs remove -v Openfiler01

To mount the nfs datastore:

esxcli storage nfs add -H -s /mnt/data01/vol01/Openfiler01/ -v Openfiler01  

I was able to create new files and access them fine. However, was unable to access the existing files on the share.

To resolve the issue, i reverted the MTU from 9000 to 1500 on the openfiler adapter and the ESXi vmkernel adapter and everything started working again.