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Understand and apply LUN masking using PSA-related commands

January 10, 2013 Objective 1 Storage No comments

What is LUN Masking?

LUN (Logical Unit Number) Masking is an authorization process that makes a LUN available to some hosts and unavailable to other hosts.LUN Masking is implemented primarily at the HBA (Host Bus Adapter) level. LUN Masking implemented at this level is vulnerable to any attack that compromises the HBA. Some storage controllers also support LUN Masking.

LUN Masking is important because Windows based servers attempt to write volume labels to all available LUN’s. This can render the LUN’s unusable by other operating systems and can result in data loss.

How to MASK on a VMware ESXi Host

Step 1: Identifying the volume in question and obtaining the naa ID
Step 2: Run the esxcli command to associate/find this naa ID with the vmhba identifiers
Step 3: Masking the volume when you want to preserve data from the VMFS volumes for later use or if the volume is already deleted
Step 4: Loading the Claim Rules
Step 5: Verify that the claimrule has loaded:
Step 6: Unclaim the volume in question
Step 7: Check Messages
Step 8: Unpresent the LUN
Step 9: Rescan all hosts
Step 10 Restore normal claim rules
Step 11: Rescan Datastores

Step 1

Check in both places as listed in the table above that you have the correct ID
Note: Check every LUN as sometimes VMware calls the same Datastore different LUN Numbers and this will affect your commands later

Example Below

Make a note of the naa ID

Step 2

Once you have the naa ID from the above step, run the following command
Note we take the : off
-L parameter will show a compact list of paths

Example below

We can see there are 2 paths to the LUN called C0:T0:L40 and C0:T1:L40
C=Channel, T=Target, L=LUN
Next we need to check and see what claim rules exist in order to not use an existing claim rule number
esxcli storage core claimrule list
Note I had to revert to the vSphere 4 CLI command as I am screenprinting from vSphere 5 not 4!

Step 3

At this point you should be absolutely clear what LUN number you are using!

Next, you can use any rule numbers for the new claim rule that isn’t in the list above and pretty much anything from 101 upwards
In theory I have several paths so i should do this exercise for all of the paths

Step 4

The Class for those rules will show as file which means that it is loaded in /etc/vmware/esx.conf but it isn’t yet loaded into runtime.

Step 5

Run the following command to see those rules displayed twice, once as the file Class and once as the runtime Class

Step 6

Before these paths can be associated with the new plugin (MASK_PATH), they need to be disassociated from the plugin they are currently using. In this case those paths are claimed by the NMP plugin (rule 65535). This next command will unclaim all paths for that device and then reclaim them based on the claimrules in runtime.

Step 7

Check Messages

See example below

Refresh the Datastore and you should see it vanish from the host view
Run the following command to check it now shows no paths
esxcfg-mpath -L | grep naa.60050768028080befc00000000000050 again will now show no paths

Step 8

Now get your Storage Team to remove the LUN from the SAN

Step 9

Rescan all hosts and make sure the Datastore has gone

Step 10

To restore normal claimrules, perform these steps for every host that had visibility to the LUN, or from all hosts on which you created rules earlier:

Run esxcli corestorage claimrule load
Run esxcli corestorage claimrule list
Note that you do not see/should not see the rules that you created earlier.

Perform a rescan on all ESX hosts that had visibility to the LUN. If all of the hosts are in a cluster, right-click the cluster and click Rescan for Datastores. Previously masked LUNs should now be accessible to the ESX hosts

Step 11

Next you may have to follow the following KB Article if you find you have these messages in the logs or you cannot add new LUNs
Run the following commands on all HBA Adapters