Error Message

# mount -o ro,mntlock=VCS,cluster,crw,delaylog,largefiles,quota,ioerror=mdisable /dev/vx/dsk/prodcnfs/export_nfs /export/nfs/prod
UX:vxfs mount.vxfs: ERROR: V-3-20: Input/output error

Filesystem was not sync prior to the umount operation and was marked as dusty

1. Check for flags on the file system.
    echo "8192B.p S" | fsdb -F vxfs /dev/vx/rdsk/prodcnfs/export_nfs| grep flag
    flags 4000 mod 0 clean 69 pflags 1                                                    <<<<  flag 69 indicates dusty.

2. As the filesystem was dusty, listing (ls -l) of the nested mount point had missing permissions on all the nodes.

Check for the directory permission of the mount point on all nodes.
     d????????? ? ?    ?       ?            ? prod                                            <<<< Notice permissions are missing.

3. Perform a lazy unmount of mount points from all nodes in cluster.
    # umount -l /export/nfs/prod                                                                

 -l : Also known as Lazy unmount. Detach the filesystem from the filesystem hierarchy now, and cleanup all references to the filesystem as soon as it is not busy anymore.

4. Again check for the directory permission of the mount point on all nodes
    drwxr-xr-x 2 root root 4096 Jan 20  2017 prod                                   <<<< Permissions are good now.

5. Mount the file system.
   # cfsmount /export/nfs/prod server102
 Mounting...
 [ /dev/vx/dsk/prodcnfs/export_nfs ] mounted successfully at /export/nfs/prod on server102

# df -h /export/nfs/prod
Filesystem                                  Size  Used Avail Use% Mounted on
/dev/vx/dsk/prodcnfs/export_nfs  4.0T  1.4T  2.6T  35% /export/nfs/prod