About snapshot methods
NetBackup can create different types of snapshots. Each snapshot type that you configure in NetBackup is called a snapshot method. Snapshot methods enable NetBackup to create snapshots within the storage stack (such as the file system, volume manager, or disk array) where the data resides. If the data resides in a logical volume, NetBackup can use a volume snapshot method to create the snapshot. If the data resides in a file system, NetBackup can use a file system method, depending on the client OS and the file system type.
Many different technologies are available for creating snapshots, and many different terms are used to refer to the underlying implementation of any given snapshot. Common terms include clone, split-mirror, and copy-on-write. In this documentation, the term "snapshot" designates any point-in-time, read-only copy of a primary volume, regardless of its underlying implementation. Method-specific terminology is explained along with specific snapshot methods in other chapters of this guide.
In some cases, more than one method can make the snapshot. If the data resides in a file system over a logical volume, NetBackup could use a file system method or logical volume method. The choice of method might depend on the snapshot features available in the storage subsystem where the data resides. Or, the choice might depend on the requirements of the snapshot method itself. For example: if the client data is in a VxFS file system over a VxVM volume, NetBackup could create the snapshot with a file system method. On the other hand, NetBackup can use a volume manager method to create the snapshot of the same data, such as VxVM or FlashSnap. Between VxVM and FlashSnap, only FlashSnap supports the Persistent FastResync feature of VxVM mirror volumes. To take advantage of the Persistent FastResync feature, you would have to select the FlashSnap method.
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