4Using The Snapshot FeatureThis chapter describes how the Snapshot feature works, lists the snapshot script commands, and explains how to usethe commands to create snapshot virtual disks. Additional information about the Snapshot feature and relateddefinitions is available in the online help, theDeployment Guide, theMD Storage Manager online help, and theOwner’sManual.The Snapshot feature creates a snapshot virtual disk that you can use as a backup of your data. A snapshot virtual diskis a logical point-in-time image of a standard virtual disk. Because it is not a physical copy, a snapshot virtual disk iscreated more quickly than a physical copy and requires less physical disk space. Typically, you create a snapshot virtualdisk so that an application, such as a backup application, can access the snapshot virtual disk. The application readsthe data while the source virtual disk remains online and user accessible. You can also create several snapshot virtualdisks of a source virtual disk and write data to the snapshot virtual disks to perform testing and analysis.NOTE: If you ordered Premium Features for the Snapshot Virtual Disks, you would have received a PremiumFeatures Activation card shipped in the same box as your Dell PowerVault MD storage array. Follow the directionson the card to obtain a key file and to enable the feature. For more information, see Premium Feature — SnapshotVirtual Disks in theOwner’s Manual.Snapshot virtual disks allow you to perform the following tasks:• Create a complete image of the data on a source virtual disk at a particular point in time.• Use only a small amount of disk space.• Provide quick, frequent, nondisruptive backups; or test new versions of a database system without affectingactual data.• Provide for snapshot virtual disks to be read, written, and copied.• Use the same availability characteristics of the source virtual disk (such as redundant array of independentdisks (RAID) protection and redundant path failover).• Map the snapshot virtual disk and make it accessible to any host on a storage area network. You can makesnapshot data available to secondary hosts for read and write access by mapping the snapshot to the hosts.• Create up to four snapshots per virtual disk.NOTE: The maximum number of snapshot virtual disks is one-half of the total number of virtual diskssupported by the RAID controller module.• Increase the capacity of a snapshot virtual disk.The following table lists the components that comprise a snapshot virtual disk and briefly describes what they do.Table 9. Snapshot Virtual Disk ComponentsComponent DescriptionSource virtual disk Standard virtual disk from which the snapshot is createdSnapshot virtual disk Point-in-time image of a standard virtual diskSnapshot repository virtual disk Virtual disk that contains snapshot metadata and copy-on-write data for a particular snapshot virtual diskThe following table lists the snapshot virtual disk commands and brief descriptions of what the commands do.45
