View source for ESXi vSphere mount LUN problems

=== cannot connect to LUN ===
Sometimes the correct LUN does not show up and trying to mount it only gives an option to format the LUN.

* 1. Log in as root to the ESX host which cannot mount the datastore using an SSH client.
* 2. Run the command:
 esxcfg-volume -l

The results appear similar to:

 VMFS3 UUID/label: 4b057ec3-6bd10428-b37c-005056ab552a/ TestDS
 Can mount: Yes
 Can resignature:  No (the volume is being actively used)
 Extent name: naa.6000eb391530aa26000000000000130c:1 range: 0 – 1791 (MB)

Record the UUID portion of the output. In the above example the UUID is 4b057ec3-6bd10428-b37c-005056ab552a.

Note: The Can mount value must be Yes to proceed with this workaround.

* 3. Run the command:
 esxcfg-volume -M <UUID>

Where the <UUID> is the value recorded in step 2.

or you can just use the label:
 esxcfg-volume -M TestDS


=== adding a new NFS LUN from the CLI ===

First list what is there:
 esxcli storage nfs list

Then add:
  esxcli storage nfs add -v NEWLUN -H 1.2.3.4 -s /mnt/newstorage
where NEWLUN is the label, -H is the host

=== adding iSCSI LUN back ===

disable snapshot LUN

 # esxcfg-advcfg -s 0 /LVM/DisallowSnapshotLun
 Value of DisallowSnapshotLun is 0
Then rescan the lot
 # esxcli storage core adapter rescan --all
 # vmkfstools -V
 # esxcli storage vmfs snapshot list
restore the default for your snapshot
 # esxcfg-advcfg -s 1 /LVM/DisallowSnapshotLun
 Value of DisallowSnapshotLun is 1
 # esxcfg-volume -l
 # df -h

The snapshot list and volumes show no results for me, but on df -h after the above commands, the ISCSI mount now shows up at the host.

 [https://kb.vmware.com/kb/2129058 vSAN handling of devices detected as snapshots (2129058)]

=== Adding a host to an NFS datastore in the VCSA errors out ===

Trying to add another host to a NFS datastore errors out and generates the error "Failed: An error occurred during host configuration".
The host should be able to connect to the NFS storage as it is allowed from the NFS server.

Digging deeper on this error gives "Operation failed, diagnostics report: Unable to get console path for volume"

In my case the host had mounted this NFS LUN before under a slightly different name and as such a now obsolete pointer somewhere was preventing the host from connecting to the LUN.

You can fix it from the CLI as follows:

First make sure the LUN isn't in the output of the following command:
 # esxcfg-nas -l

If that's not the case then proceed and try to add the LUN from the CLI.
If your host is 10.0.0.5 and the NFS share on it is /mnt/vol/share which you want to mount as MYLUN then add like
 # esxcfg-nas -a -o 10.0.0.5 -s /mnt/vol/share MYLUN
  Error performing operation: Unable to add new NAS, volume with the label MYLUN already exists
Here the vSphere server is indeed complaining that MYLUN exists.
Run:
 # df -h
and verify that it is NOT in the list.
After that test you can remove the LUN
 # esxcfg-nas -d MYLUN
 IORM: failed to disable IORM: Unable to get console path for volume, MYLUN
 NAS volume MYLUN deleted.
Now you can rerun the above command:
 # esxcfg-nas -a -o 10.0.0.5 -s /mnt/vol/share MYLUN
 Connecting to NAS volume: MYLUN
 MYLUN created and connected.

=== iSCSI shows as normal, degraded ===

In vSphere 6.5 this happens when you have only 1 uplink.