vsphere-esxi-vcenter-server-55-storage-guide

Chapter 16 Working with DatastoresManaging Duplicate VMFS DatastoresWhen a storage device contains a VMFS datastore copy, you can mount the datastore with the existingsignature or assign a new signature.Each VMFS datastore created in a storage disk has a unique signature, also called UUID, that is stored in thefile system superblock. When the storage disk is replicated or its snapshot is taken on the storage side, theresulting disk copy is identical, byte-for-byte, with the original disk. As a result, if the original storage diskcontains a VMFS datastore with UUID X, the disk copy appears to contain an identical VMFS datastore, or aVMFS datastore copy, with exactly the same UUID X.In addition to LUN snapshotting and replication, the following storage device operations might cause ESXito mark the existing datastore on the device as a copy of the original datastore:• LUN ID changes• SCSI device type changes, for example, from SCSI-2 to SCSI-3• SPC-2 compliancy enablementESXi can detect the VMFS datastore copy and display it in the vSphere Web Client. You have an option ofmounting the datastore copy with its original UUID or changing the UUID to resignature the datastore.Whether you chose resignaturing or mounting without resignaturing depends on how the LUNs aremasked in the storage environment. If your hosts are able to see both copies of the LUN, then resignaturingis the recommended method. Otherwise, mounting is an option.Keep Existing Datastore Signature in the vSphere Web ClientIf you do not need to resignature a VMFS datastore copy, you can mount it without changing its signature.You can keep the signature if, for example, you maintain synchronized copies of virtual machines at asecondary site as part of a disaster recovery plan. In the event of a disaster at the primary site, you mountthe datastore copy and power on the virtual machines at the secondary site.Prerequisites• Perform a storage rescan on your host to update the view of storage devices presented to the host.• Unmount the original VMFS datastore that has the same UUID as the copy you plan to mount. You canmount the VMFS datastore copy only if it does not collide with the original VMFS datastore.• Browse to Datastores in the vSphere Web Client navigator. See “Display Datastore Information in thevSphere Web Client,” on page 22.Procedure1 Click the Create a New Datastore icon.2 Type the datastore name and if required, select the placement location for the datastore.3 Select VMFS as the datastore type.4 From the list of storage devices, select the device that has a specific value displayed in the SnapshotVolume column.The value present in the Snapshot Volume column indicates that the device is a copy that contains acopy of an existing VMFS datastore.5 Under Mount Options, select Keep Existing Signature.6 Review the datastore configuration information and click Finish.VMware, Inc. 141