Does the Datastore UUID Change Across Host clusters or vCenters?
I had someone reach out to me regarding the UUID of a VMFS datastore. The context was the customer has an application that is aware of the datastore's signature and they want to migrate the application to a new host cluster. They wanted to make sure the datastore details didn't change if the datastore was temporarily mounted to multiple host clusters to facilitate the migration.
Question: If a datastore is mounted to a new host cluster or even a new vCenter, will the signature (UUID) change for that datastore?
Answer: The dataStore UUID for both VMFS and vVols is unique to a given datastore, so no matter where you expose that datastore it will have the same UUID.
When a VMFS datastore is created, the UUID is stamped into the VMFS volume header. For vVols the UUID is created and associated with the storage container, so no matter where you see that storage container you will get that same UUID. The only way this can change is if you were to re-signature the datastore or if you were to delete and recreate a new completely LUN/storage container and datastore. When the identifier is created, it uses some of the physical device identifiers from the array. With that said, you cannot create a new datastore and have it get the same UUID as an old one. The UUIDs are globally unique identifiers and when you create them they depend on time/date and get their uniqueness as part of that. Subsequently, you should never re-use a UUID as the system expects to never see a duplicate.
The UUID for a datastore is unique to each datastore and has no relation to the vCenter. Thus it will not change across vCenters and as such, both vVols and VMFS datastores can be shared across vCenters.
An example of needing to re-signature a datastore is if the datastore is copied and you want to retain the data stored on the VMFS datastore copy. Another example would be DR replication of a datastore. Below are some links to resources in the event you may need to resignature a datastore.
- vSphere VMFS Datastore Copies and Datastore Resignaturing (vmware.com)
- Mount a VMFS Datastore Copy (vmware.com)
- Managing Duplicate VMFS Datastores (vmware.com)
- Resignature a VMFS Datastore Copy (vmware.com)
- Keep Existing Datastore Signature (vmware.com)
- Best Practices for Fibre Channel Storage with ESXi (vmware.com)
- Troubleshooting LUNs detected as snapshot LUNs in vSphere (1011387) (vmware.com)
- fault.VmfsAlreadyMounted error when resignaturing a snapshot LUN (2082643) (vmware.com)
- Re-signature operation of snapshot LUN is failing with fault: VmfsAlreadyMounted. (76989) (vmware.com)
Thanks to Thor Jensen, one of our Sr. storage engineers for the detailed insight.