Why can't I add these LUNs without formatting?

Posted on 2010-08-19
Last Modified: 2013-11-14
I had to do a lot of work on our SAN/ESX server setup last night. And among it, something broke. As it is I was able to add the LUNs back to one ESX 4.1 host, and get all production servers up. However, the other 2 nodes can SEE the iSCSI targets and connect to them. They see the LUNs perfectly. However, they do not see the VMFS partition. So I am unable to add them to the other 2 nodes. The option to use the existing signature or re-signature them is greyed out. The only option that I have available is format. These same Luns are working perfectly on another node with identical hardware and an identical fresh install of ESX 4.1. WTF!? Why can't the other nodes use them?
Question by:CCB-Tech
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LVL 23

Assisted Solution

by:Luciano Patrão
Luciano Patrão earned 100 total points
ID: 33481059

First how are connecting(on storage side) the SAN/LUNs to this hosts?


Author Comment

ID: 33481119
They are iSCSI connections. 2 gigabit connections that are setup with Round Robin. They do NOT connect via a switch. They are connected directly from the node to the SAN host via CAT6. The SAN host is Open-E. These machines have been working in the past, but I don't know what happened to cause the problem.
LVL 28

Expert Comment

ID: 33481639
I guess I will ask the dumb question and did your rescan (not refresh) your storage adapters on the other two hosts?

If you have look at these two articles:;jsessionid=207105C7CC694F34D4621ECDFFCC262B

Good Luck
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Accepted Solution

Draiocht earned 200 total points
ID: 33483102
Try this
1 Log in to the vSphere Client and select the server from the inventory panel.
2 Click the Configuration tab and click Storage in the Hardware panel.
3 Click Add Storage.
4 Select the Disk/LUN storage type and click Next.
5 From the list of LUNs, select the LUN that has a datastore name displayed in the VMFS Label column and
click Next.
The name present in the VMFS Label column indicates that the LUN is a copy that contains a copy of an
existing VMFS datastore.
6 Under Mount Options, select Keep Existing Signature.
7 In the Ready to Complete page, review the datastore configuration information and click Finish.

Author Comment

ID: 33485494
@bgoering - I have tried multiple rescans for both new LUNs and VMFS. Not a dumb question at all, and believe me, I wish it was that simple. I'm checking through those articles. They look like they might help. Any idea WTF is going on?

@Draiocht - This is the problem I am having. When I try to add any of them both the "Keep Signature" and "Assign New Signature" options are greyed out. The only option available is "Format Disk."

Author Comment

ID: 33485934
Is there any danger to the data contained on the LUNs if I use the disallowsnapshotLUN=0 flag?
LVL 28

Assisted Solution

bgoering earned 200 total points
ID: 33486345
I wouldn't think so, but take a look at for a detailed discussion. From that article:

"According to the San Config Guide(vi3_35_25_san_cfg.pdf) there are three states:

1.EnableResignature=0, DisallowSnapshotLUN=1 (default)
In this state, you cannot bring snapshots or replicas of VMFS volumes by the array into the ESX Server host regardless of whether or not the ESX Server has access to the original LUN. LUNs formatted with VMFS must have the same ID for each ESX Server host.
2.EnableResignature=1, (DisallowSnapshotLUN is not relevant)
In this state, you can safely bring snapshots or replicas of VMFS volumes into the same servers as the original and they are automatically resignatured.
3.EnableResignature=0, DisallowSnapshotLUN=0 (This is similar to ESX Server 2.x behavior.)
In this state, the ESX Server assumes that it sees only one replica or snapshot of a given LUN and never tries to resignature. This is ideal in a DR scenario where you are bringing a replica of a LUN to a new cluster of ESX Servers, possibly on another site that does not have access to the source LUN. In such a case, the ESX Server uses the replica as if it is the original."

After reading through all of this article (I personally have never had to do this) I would first check on something before changing this setting. Look at the SCSI LUN number being presented and make sure it is the same for each server. So if the iSCSI is presenting LUN A as SCSI ID 2 on the host that it is working on, make sure it is presented as SCSI ID 2 to the remaining hosts. That would be configuration on the storage server side. The way I read it is that maybe it is seeing the LUN as SCSI ID 3 or something, and the vmfs header says it should be 2, so won't recognize it as valid.

In all of my environment I have always kept them the same so haven't run into the issue. I did read by changing that setting it allowed the filesystem to be imported and used, and is probably safe. At least my research has not turned up anyone reporting any ill effects from doing that. But if it were me I would check that the presentation of the LUNs are consistent across all of the boxes first, then change the setting if that didn't work.

Good Luck

Author Comment

ID: 33486677
Thanks for the help man! I'm going to have to wait until tomorrow night to do any testing, but I had to do some work with our SAN dealer today. I believe you hit the nail on the head though. The LUN ids are correct across the board. HOWEVER, that was one thing I changed the other night. Part of what I've got to do this weekend will involve a purge of the iSCSI targets and a recreation of them. So IMO that will likely fix it. We'll see!
LVL 28

Expert Comment

ID: 33487252
Sounds good - keep me posted

Author Comment

ID: 33571305
I'm currently working with our SAN developer (Open-E) to get the problem resolved. We're not sure of the cause nor what to do further. I can't even get it to work with SCST. I will update this once I have more information.

Author Comment

ID: 33571329
After the rebuild I was able to get all LUNs viewable. It seems the easiest way to remedy this was to absolutely remove everything about the iSCSI targets in VMware. Then remove everything about the targets in the SAN itself. Then create new fresh targets. The add them back to VMware. That seemed to do the trick. Thanks for your help as always man!

Author Closing Comment

ID: 33571344
I had to do a full recreation of the targets, but using the information here I was able to make them work in the interiem.

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