VMware wants to format an existing VMFS

We are running two VMware ESXi v4 systems. We access our VMs on a NAS via iSCSI. Recently, we had some issues and had to remove and reconfigure the iSCSI LUN on each server. On one, it came right up. We were able to see the LUN and it mounted just fine and we saw all of our VMs. On the second VMware ESXi box, if we do a Rescan.. it won't auto-mount the LUN (which has VMFS). If we do an Add Storage, we can find the LUN but then we get only the option "Format the disk [create a new datastore]).

Obviously that would be a bad idea. :)

I can't figure out the problem.

BTW, we can mount a second LUN on both VMware servers just fine that we use for some other VMs that we just created.
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Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization ConsultantCommented:
can you mount this LUN on the other ESX servers?

no one has presented this to A Windows source and formatted it?
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization ConsultantCommented:
could you explain what reconfuguration you did on the LUNs?
Danny McDanielClinical Systems AnalystCommented:
Is the option to re-signature available when you go through add storage wizard?

if you can, post a screenshot of what you see during add storage wizard
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Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization ConsultantCommented:
if seems that for some reason the signature on the LUN has changed. Hence VMware ESXi, wants to reformat, rather than add.

check at the ESXi console with

esxcfg-volume -l

Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization ConsultantCommented:
You can also re-signature existing VMFS volumes through the vSphere client using the "Add Storage" wizard in the host configuration tab storage section.

The wizard detects the existing VMFS volume and lets you choose between:

- Re-signature volume and keep data.

- Keep existing signature and mount the volume.

- Reformat the volume.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization ConsultantCommented:
If this LUN is used on other ESXi servers, keep the signature.
puryear-itAuthor Commented:
Let's clarify a few things just in case.

The LUN is being exported by a NAS that offers iSCSI.
vm-4 is able to mount the LUN just fine and sees the filesystem and VMs.
vm-3 wants to format the LUN.

I am attaching screenshots to make life easier. :)

Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization ConsultantCommented:
okay. got it.

what output do you get with esxcfg-volume -l

also do you have valid backups of the vms on the lun.
puryear-itAuthor Commented:
on vm-3:

~ # esxcfg-volume -l
VMFS3 UUID/label: 4cc89503-f054d0d4-2865-00221958e471/nas3-vmfs
Can mount: Yes
Can resignature: No (the volume is being actively used)
Extent name: naa.600140588e9bab7d2b7ed4b53dadc1de:1     range: 0 - 1048319 (MB)

The volume is mounted on vm-4, but that's common practice with vmfs. Or perhaps I'm missing something.
Danny McDanielClinical Systems AnalystCommented:
in the gui, do a rescan on all storage, then review the /var/log/vmkernel file for errors.  

'less /var/log/vmkernel' will open it, do a capital G to go to the bottom of the file, then use the page-up/page-down keys to navigate.  Look for any error messages, especially those that reference that naa id or UUID.  post the file up if you can, too.  You can download it with winscp or cp it over to a working datastore and then use the datastore browser to download it to your pc.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization ConsultantCommented:
could try

esxcfg-volume -m 4cc89503-f054d0d4-2865-00221958e471


esxcfg-volume -m nas3-vmfs

and see if you get an error, this is the equivalent of the gui mount option.

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puryear-itAuthor Commented:
Sorry. Give me a little more time. Thanks.
puryear-itAuthor Commented:
Wow. Worked perfectly:

# esxcfg-volume -m 4cc89503-f054d0d4-2865-00221958e471

There you go. Sometimes the CLI just works better. :)
puryear-itAuthor Commented:
Very helpful and to the point. Took the time to read through my initial question and my responses and gave me the absolute right answer.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization ConsultantCommented:
We also use the command line, rather than the GUI, because it's more powerful, or I'm I just old fasioned, and not a GUI man!
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization ConsultantCommented:
Glad it's resolved, and that issue is more common than you think!
puryear-itAuthor Commented:
Yeah, I wrote an internal KB for this issue based on this EE thread. Thanks!
~ # esxcfg-volume -M VOLUME_LABEL_OR_ID

My issue was slightly different, but for those that wander here and find the above solution doesn't work. Try a capital 'M'.

It is a different command and resolved my issue. Same premise as the OP but nothing else worked.  
I have the same problem

I tried with all the option but still i couldnt mount the LUN. I could see the LUN displayed in


But I couldnt mount this, when i attempt to mount, it says that it is going to format all data.

My ESXi version is 4.0.0, 208167

Check the screenshot for more info,


fdisk -u result

Disk /vmfs/devices/disks/naa.60a98000534b48716d346a42476b3576: 483.1 GB, 483183820800 bytes
255 heads, 63 sectors/track, 58743 cylinders, total 943718400 sectors
Units = sectors of 1 * 512 = 512 bytes

                                                    Device Boot      Start         End      Blocks  Id System
/vmfs/devices/disks/naa.60a98000534b48716d346a42476b3576p1           128 943706294 471853083+  fb  VMFS

There is data I am afraid to proceed further...
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