50 Planning: MD3200 Series Storage Array Terms and Conceptsonline and user-accessible. When the backup is completed, the snapshotvirtual disk is no longer needed. You can create up to four snapshots pervirtual disk.Snapshots are used to recover previous versions of files that have changedsince the snapshot was taken. Snapshots are implemented using a copy-on-write algorithm, which makes a backup copy of data the instant an erroroccurs. Data on a virtual disk is copied to the snapshot repository before it ismodified. Snapshots are instantaneous and take up less overhead than a fullphysical copy process.Snapshot Repository Virtual DiskWhen you create a snapshot virtual disk, it automatically creates a snapshotrepository virtual disk. A snapshot repository is a virtual disk created in thestorage array as a resource for a snapshot virtual disk. A snapshot repositoryvirtual disk contains snapshot virtual disk metadata and copy-on-write datafor a particular snapshot virtual disk. The repository supports one snapshotonly.You cannot select a snapshot repository virtual disk as a source virtual disk oras a target virtual disk in a virtual disk copy. If you select a Snapshot sourcevirtual disk as the target virtual disk of a virtual disk copy, you must disable allsnapshot virtual disks associated with the source virtual disk.CAUTION: Before using the Snapshot Virtual Disks Premium Feature in aWindows® Clustered configuration, you must map the snapshot virtual disk to thecluster node that owns the source virtual disk. This ensures that the cluster nodescorrectly recognize the snapshot virtual disk.Mapping the snapshot virtual disk to the node that does not own the sourcevirtual disk before the snapshot enabling process is completed can result inthe operating system incorrectly identifying the snapshot virtual disk. Thiscan result in data loss or an inaccessible snapshot.For details on mapping the snapshot virtual disk to the secondary node, referto the Dell™ PowerVault™ MD3200 and MD3220 Storage Arrays WithMicrosoft® Windows Server® Failover Clusters on support.dell.com/manuals.
