Managing VMFS Volume Copies (Resignaturing)

By default, ESX/ESXi hosts mount all VMFS datastores. Each VMFS datastore that is created in a partition on a LUN has a unique UUID that is stored in the file system superblock. In addition, the LUN ID of the source LUN is unique and is stored in the VMFS metadata.

When a LUN is replicated or a copy is made, the resulting LUN copy is identical, byte-for-byte, with the original LUN. As a result, if the original LUN contains a VMFS datastore with UUID X, the LUN copy appears to contain an identical VMFS datastore, or a VMFS datastore copy, with exactly the same UUID X. ESX/ESXi can determine whether a LUN contains the VMFS datastore copy, and considers the copy unresolved and does not mount it automatically.

To make the data on the LUN copy available, you can either force mount the copy if you are sure the original is not in use, or you can resignature the copy. When you perform datastore resignaturing, consider the following points:

■	Datastore resignaturing is irreversible because it overwrites the original VMFS UUID.

■	The LUN copy that contains the VMFS datastore that you resignature is no longer treated as a LUN copy, but instead appears as an independent datastore with no relation to the source of the copy.

■	A spanned datastore can be resignatured only if all its extents are online.

■	The resignaturing process is crash and fault tolerant. If the process is interrupted, you can resume it later.

■	You can mount the new VMFS datastore without a risk of its UUID colliding with UUIDs of any other datastore, such as an ancestor or child in a hierarchy of LUN snapshots.

See the vSphere Storage documentation for additional information.

The easiest way to resignature unresolved volumes is by using the HostDatastoreSystem.ResignatureUnresolvedVmfsVolume_Task method. The method assigns a new DiskUuid to a VMFS volume, but keep its contents intact. The method supports safe volume sharing across hosts and is appropriate in most cases.

You can instead use the low-level HostStorageSystem methods to find, force mount, or unmount unresolved volumes:

■	HostStorageSystem.QueryUnresolvedVmfsVolume – Obtains the list of unbound VMFS volumes. For sharing a volume across hosts, a VMFS volume is bound to its underlying block device storage. When a low-level block copy is performed to copy or move the VMFS volume, the copied volume is unbound.

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HostStorageSystem.ResolveMultipleUnresolvedVmfsVolumes – Resignatures or force mounts unbound VMFS volumes. This method takes a HostUnresolvedVmfsResolutionSpec data object as input. The HostUnresolvedVmfsResolutionSpec.resolutionSpec property is an array of HostUnresolvedVmfsResolutionSpec data objects that contain a HostUnresolvedVmfsResolutionSpecVmfsUuidResolution enumeration. The enumeration is either forceMount or resignature.

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UnmountForceMountedVmfsVolume – Unmounts a force mounted VMFS volume. When a low-level block copy is performed to copy or move the VMFS volume, the copied volume is unresolved. For the VMFS volume to be usable, a resolution operation is applied. As part of resolution operation, you might decide to keep the original VMFS UUID. Once the resolution is applied, the VMFS volume is mounted on the host for its use. This method allows you to unmount the VMFS volume if it is not used by any registered virtual machines.