In the Computer and Storage World a snapshot is the state of a system at a particular point in time. More in detail, a snapshot is a point-in-time, read-only, disk-based copy of a client volume (see Blog Link).
In the backup world, after the snapshot is created, NetBackup backs up data from the snapshot, not directly from the client’s primary or original volume. Users and client operations can access the primary data without interruption while data on the snapshot volume is being backed up. The contents of the snapshot volume are cataloged as if the backup was produced directly from the primary volume. After the backup is complete, the snapshot-based backup image on storage media is indistinguishable from a backup image produced by a traditional, non-snapshot backup.
NetBackup Snapshot Client Tecnology providing high performance, low impact protection features and:
- Enabled through NetBackup Snapshot Client allows customers to use either host or array-based snapshots methods
- Access a variety of hardware and software snapshot-based technologies via a single client
- Combine with Application & Database Pack to enable off-host application backups
What are the snapshots type that NetBackup Snapshot Client can provide to the customer? NetBackup provides a variety of snapshot-based features and 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.
Clone, split-mirror, and copy-on-write are common term that we used ever day to refer to snapshot technology. If we wnat to generate a snapshot we could use more than one method; if the client data is in a VxFS file system over a VxVM volume, NetBackup could create the snapshot with a file system method, or alternatively NetBackup could use a volume manager method to create the snapshot of the same data, such as VxVM or FlashSnap (FlashSnap combines the speed of raw-partition backups with the ability to restore individual files).
It is clear that we have more methods to generate a snapshot, but we must also take in mind that these method relies on the snapshot technology that is built into the storage subsystem where the data is stored. To laverage this technology build into the Storage subsystem we need of libraries that enable the cominucation between Netbackup and the Subsystem; Netbackup provides this Libraries, called snapshot providers and a document called NetBackup (tm) 7 Snapshot Client Compatibility that lists all the supported third-party devices.
Considering the high volume of storage vendor and storage subsystems on the market, we can consult a document contains information for Symantec NetBackup 7.x. (NetBackup Server, Client, and Snapshot Client) . Each major section (that is, Arrays, Agents, OSes, VSS providers) represents the same data, but sorted differently. These sections can be accessed by expanding the bookmarks on the left.
- Through the Netbackup console, on the NetBackup policy tab, you specify the method you want to use. When the policy runs, the snapshot method calls the snapshot provider library. The Library then accesses the underlying commands in the storage subsystem to create the snapshot.
- A complete guide about the NetBackup Snapshot Cliemnt facilities can be found in the Yellow Book, at the following address with other book that provide technical know-how about Symantec technology .
-  NetBackup Enterprise Server Guide
-  NetBackup Enterprise Server Compatibility List