vDCA550-Objective 1.1–5-Understand and apply VMFS re-signaturing

Every VMFS datastore has a universal unique identifier (UUID), which is used to match a LUN to a specific VMFS datastore. The UUID signature is a hexadecimal number that is shown in Figure 3-10. One way to think of the UUID or signature of the datastore is how a MAC address is a unique identifier for a network interface. A UUID signature is a way to provide uniqueness for a LUN to associate with a particular datastore.

You can find the UUID of a VMFS datastore by following command

#vmkfstools –P –h datastore name
where  (-P =queryfilesystem , -h = human readable)

Below is the example to find the ISCSI1_DataStore UUID.


Why we need to resignature VMFS Volume (Use case)?

  • When a LUN is copied or a replication made of an original LUN, the copied LUN ends up being absolutely identical to the original LUN including having the same UUID. This means the newly copied LUN must be resignatured before it is mounted. ESXi can determine whether a LUN contains a VMFS copy and does not mount it automatically.
  • A change in the host LUN or SCSI device type causes the VMFS volume’s UUID to require a new signature

NOTE: NFS datastore’s inode resides on the storage device; it does not have a UUID

Things to Know:

  1. Creating a new signature for a drive is irreversible
  2. VM Stored in resignatured datastore require to re-add in the inventory.


  • From vSphere Classic Client
  • Click Configuration > Storage ->Click “Add Storage” in the right window frame
  • Select Disk/LUN -> click “Next”
  • Select the device to add  -> click “Next”
  • You then have following “3” options


  1. Keep the existing signature: This option will leave the VMFS partition unchanged
  2. Assign a new signature: This option will delete the existing disk signature and replace it with a new one. This option must be selected if the original VMFS volume is still mounted (It isn’t possible to have two separate volumes with the same UUID mounted simultaneously)
  3. Format the disk: This option is the same as creating a new VMFS volume on an empty LUN
  • Choose your desired resignature option->click “Next”
  • Review your changes -> click “Finish”



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