Configuration: Premium Feature—Virtual Disk Copy 171formatted with a journaling file system, any attempt to issue a read request tothe source virtual disk may be rejected by the storage array RAID controllermodules and result in an error message. Make sure that the Read-Onlyattribute for the target virtual disk is disabled after the virtual disk copy iscomplete to prevent error messages from being displayed.Online CopyAn online copy creates a point-in-time snapshot copy of any virtual diskwithin a storage array, while still allowing writes to the virtual disk when thecopy is in progress. This is achieved by creating a snapshot of the virtual diskand using that snapshot as the actual source virtual disk for the copy. In anonline virtual disk copy, the relationship is between a snapshot virtual diskand a target virtual disk. The virtual disk for which the point-in-time image iscreated (the source virtual disk) must be a standard virtual disk in the storagearray.A snapshot virtual disk and a snapshot repository virtual disk are createdduring the online copy operation. The snapshot virtual disk is not an actualvirtual disk containing data; instead, it is a reference to the data contained onthe virtual disk at a specific time. For each snapshot taken, a snapshotrepository virtual disk is created to hold the copy-on-write data for thesnapshot. The snapshot repository virtual disk is used only to manage thesnapshot image.Before a data block on the source virtual disk is modified, the contents of theblock to be modified are copied to the snapshot repository virtual disk.Because the snapshot repository virtual disk stores copies of the original datain those data blocks, further changes to those data blocks write only to thesource virtual disk.NOTE: If the snapshot virtual disk that is used as the copy source is active, thesource virtual disk performance degrades due to copy-on-write operations. Whenthe copy is complete, the snapshot is disabled and the source virtual diskperformance is restored. Although the snapshot is disabled, the repositoryinfrastructure and copy relationship remain intact.
