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Application-Aware Writer

Using this Protected Item type may incur a Booster charge.

About

VSS is a technology for taking a consistent point-in-time snapshot of a disk volume. A VSS Writer is an extra software plugin that detects when this action is taking place and ensures that application-specific files are in a safe state on disk. Comet's "Application-Aware Writer" feature allows you to invoke a single VSS Writer, or a sub-component of a single VSS Writer, and back up only the files that it was protecting.

This is also an important third-party integration point for application vendors. If your third-party application includes a VSS Writer, you can use this Protected Item type to back it up using Comet.

Some products that can be backed up with this Protected Item type are:

  • Oracle DB;
  • MailStore Server;
  • Microsoft Dynamics CRM;
  • Microsoft SharePoint;
  • Pervasive PSQL (Actian Zen);
  • other products natively supported by Comet, including Microsoft Exchange Server, Microsoft Hyper-V, and Microsoft SQL Server;
  • and other products.

In early versions of Comet, this Protected Item type was named "VSS-Aware Component".

NOTE: This Protected Item type is intended for integration with specific custom applications. If you want to back up normal files with a VSS snapshot, use the "Files and Folders" Protected Item type with the "take filesystem snapshot" option enabled.

Selecting components

In Comet Backup, click the Edit button (pencil icon) to browse the available VSS Writers installed on your device.

You can select the top-most checkbox to include all components within the VSS Writer, or you can select individual components within the VSS Writer. For instance, the Microsoft SQL Server VSS Writer allows you to select individual databases for backup.

The VSS Writer itself may mark some components as non-selectable. This is shown in Comet as a grey subcomponent without a checkbox.

VSS Mode

You can perform the operation in "VSS Full", "VSS Copy", "VSS Incremental", or "VSS Differential" modes. If a specific VSS Writer does not support the selected backup mode, it will perform the backup in "Full" mode.

The actual behavior of these modes is specific to each VSS Writer. For more information, consult the documentation for your VSS Writer.

The modes are a set of general-purpose options that each VSS Writer can implement in different ways. We would recommend that you set it to the same mode as you had it for your regular backup job, usually either 'Full' or 'Copy'.

Backing up Oracle Database

Comet can back up the contents of any installed VSS Writer using the "Application Aware Writer" option. Oracle Database officially supports backup via its installed VSS Writer.

You may need to install the Oracle VSS Writer separately. It is available with Oracle Database 11g and later (including 12c and 18c); newer versions of the Oracle VSS Writer can be installed separately to back up a 10g or 9i database.

You should use the "Application Aware Writer" option and select the Oracle VSS Writer - ORCL component. Inside this option, you can select individual tablespaces for backup, or select the entire component.

The Oracle VSS Writer reads the database with SYSDBA privileges.

The Oracle VSS Writer supports log, copy, full, differential, and incremental backups.

  • "Full" or "Copy" backups at the VSS component will allow Comet to deduplicate them together, producing its own incremental backups
  • a "VSS FULL" backup will take the full database, and all log files, [and possibly truncate the logs(1)];
  • a "VSS COPY" backup will take the full database, all log files, [and possibly not truncate the logs (2)];
  • a "VSS Incremental" backups at the VSS component may be slightly more space-efficient than Comet's incremental system, as Oracle has more specific understanding of the file formats. When restoring, you must take care to restore the full backup and all incremental/log backups too, that adds complexity.

(1), (2) Truncating the logs is specifically how MS SQL handles the mode. Oracle DB may handle modes in a different manner, and may not truncate.

More information about the Oracle VSS Writer is available in Oracle's documentation.

Backing up MS SQL Database

The MS SQL VSS Writer supports log, copy, full, differential, and incremental backups.

  • "Full" or "Copy" backups at the VSS component will allow Comet to deduplicate them together, producing its own incremental backups
  • a "VSS FULL" backup will take the full database, and all log files, and truncate the logs;
  • a "VSS COPY" backup will take the full database, all log files, and not truncate the logs, useful if you have two backup systems running since truncation will apply to everyone;
  • a "VSS Incremental" backups at the VSS component may be slightly more space-efficient than Comet's incremental system, as Oracle has more specific understanding of the file formats. When restoring, you must take care to restore the full backup and all incremental/log backups too, that adds complexity.