Data Backup
The chapter Logging, Backup, and Restore in Advanced Operations Guide discusses the data backup solutions provided with Pervasive PSQL. In addition to those solutions, Pervasive PSQL Vx Server includes the following:
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Pervasive Backup Agent
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Pervasive PSQL VSS Writer
If your backup software is not aware of the Microsoft Volume Shadow Copy Service (VSS), you can use Pervasive Backup Agent with your backup software. The VSS framework is included with Windows Server 2003 and newer operating systems.
If your backup software is VSS aware, Pervasive PSQL VSS Writer is automatically invoked during VSS backups. You do not need to use Pervasive Backup Agent if you backup software is already VSS aware.
Pervasive PSQL VSS Writer and Pervasive Backup Agent can be used together, but there is no advantage in doing so. Your backup process will be more streamlined if you select one method or the other.
Pervasive Backup Agent
Pervasive Backup Agent is an optional product included with Pervasive PSQL Vx Server. By default, it is not installed. If you want to install Backup Agent, you must install it from the Pervasive PSQL Vx Server media after you install Pervasive PSQL Vx Server. Select Pervasive Backup Agent on the installation selection dialog. No separate license for Pervasive Backup Agent is required if it is installed on the same machine as Pervasive PSQL Vx Server.
Pervasive Backup Agent provides a quick and simple method for you to set and manage continuous operations on your Pervasive PSQL database files. Setting and managing continuous operations is a critical piece when backing up your Pervasive PSQL databases without using Microsoft Volume Shadow Copy Service (VSS). Backup Agent automatically handles setting and managing continuous operations on your open files so that your data is still available from your application during your backup. Once the backup procedure is complete, stopping Backup Agent automatically takes the files out of continuous operations and rolls in all the changes captured during the backup.
Pervasive Backup Agent is compatible with many popular backup applications on the market. Note that the backup application must be able to issue commands to start and stop other applications (so that the commands can start and stop Pervasive Backup Agent).
For details on Pervasive Backup Agent, see Pervasive Backup Agent Guide.
Pervasive PSQL VSS Writer
The Microsoft Volume Shadow Copy Service (VSS) consists of Writer, Provider, and Requestor components. Pervasive PSQL Vx Server supports VSS with only a Writer component, Pervasive PSQL VSS Writer. Pervasive PSQL VSS Writer is a feature of the database engine and is available for use after Pervasive PSQL Vx Server is installed. Pervasive PSQL VSS Writer is available only on Windows operating systems.
(For more information on Volume Shadow Copy Service, refer to the Microsoft Web site document, A Guide for SQL Server Backup Application Vendors.)
Overview
During VSS snapshots, Pervasive PSQL VSS Writer quiesces all disk I/O write activity to all Pervasive PSQL data and transaction log files, regardless of the volume on which they reside. After the snapshot is taken, Pervasive PSQL VSS Writer allows all disk I/O to resume; this includes any writes that were deferred during the quiesced period.
Pervasive PSQL VSS Writer never quiesces disk I/O read activity allowing normal database processing to continue during the quiesced period as long as writes are not required. Pervasive PSQL VSS Writer operates normally during the backup phase, although performance will likely be reduced due to the backup activity of the VSS service and VSS Requestor.
The Microsoft Volume Shadow Copy facility allows Backup and Restore products to create a shadow copy for backup in which the files are either in one of the following states:
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Well-defined and consistent state
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A crash-consistent state (possibly not suitable for a clean restore)
Files in the VSS snapshot will be in the well-defined and consistent state if all of the following are true:
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The file’s writer is VSS-aware
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The Backup and Restore product recognizes and notifies the VSS-aware writer to prepare for a snapshot
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The VSS-aware writer successfully prepares for the snapshot
Otherwise the writer’s files are backed up in the crash-consistent state.
VSS Writer Details
The following items discuss specifics about Pervasive PSQL VSS Writer.
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Supported Operating Systems
The same Windows operating systems on which Pervasive PSQL Server is supported also support Pervasive PSQL VSS Writer. The VSS framework is included with Windows Server 2003 and newer operating systems.
Pervasive PSQL VSS Writer is functional on the same bitness as the machine’s operating system and the Pervasive PSQL installed. Pervasive PSQL VSS Writer (32-bit) is only supported on 32-bit machines, and 64-bit is only supported on 64-bit machines. If the bitness does not match, Pervasive PSQL functions properly, but the VSS Writer is unavailable.
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Supported Backup Types
Pervasive PSQL VSS Writer supports manual or automatic backups of data volumes. Pervasive PSQL VSS Writer is supported on Full and Copy Volume backups. Incremental, Differential, and Log backups are not supported. VSS recognizes Pervasive PSQL VSS Writer as a component. However, Pervasive PSQL VSS Writer does not support component backups. If the VSS Requestor does call Pervasive PSQL VSS Writer in a component backup, the VSS Writer performs the same actions as in a Full or Copy Volume backup.
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Virtualized Environment Support
Pervasive PSQL VSS Writer supports VSS Requesters that trigger VSS backups in virtualized environments. Performing a VM snapshot does not invoke a VSS backup.
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Multiple Volume Pervasive PSQL Data Files
Pervasive PSQL files and transaction logs may reside on multiple volumes. When backing up Pervasive PSQL files, remember that the transaction logs and related files on other volumes should be backed up simultaneously. Files that are independent of each other may not need to be backed up at the same time as non-related Pervasive PSQL files.
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Backup Solution Compatibility
To determine if a particular Backup and Restore product recognizes the Pervasive PSQL VSS Writer and that it will notify the writer to prepare for a snapshot, start a backup with the product. After the backup is in progress, consult the pvsw.log to determine if the PSQL VSS Writer logged the Frozen or Thawed states. If the Backup and Restore product did not notify the PSQL Writer to prepare for the backup, another solution such as the PSQL Backup Agent must be used in order to backup PSQL data files in the well-defined and consistent state.
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Pervasive PSQL VSS Writer and Restore Operations
Stop the Pervasive PSQL services prior to performing a Restore operation with the Backup software. Failure to do so causes the VSS Writer to inform the VSS Requestor that it cannot participate in the restore. Transaction logs will need to be restored along with the data files to guarantee the integrity of the data. If Pervasive PSQL data and transaction log files are restored while Pervasive PSQL is running, the results are unpredictable and could lead to data corruption.
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Pervasive PSQL VSS Writer and Pervasive Continuous Operations
You may have an existing backup process that already uses Pervasive Continuous Operations or Pervasive Backup Agent. If you choose, you can continue to use that process with Pervasive PSQL Vx Server and Pervasive PSQL VSS Writer. Pervasive PSQL VSS Writer does not interfere with Continuous Operations or Backup Agent. However, there is no advantage to using both Pervasive PSQL VSS Writer and Continuous Operations (or Backup Agent) together. Your backup process will be more streamlined if you select one method or the other.
When Pervasive PSQL VSS Writer is called and files are in Continuous Operations, be aware that VSS Writer operates independently from any Continuous Operations. If files are in Continuous Operations when a VSS backup is in progress, view PVSW.LOG after the backup completes. Ensure that the Frozen and Thawed states completed successfully and that the data is in a well-defined and consistent state.
Also note that Pervasive PSQL VSS Writer requires the Microsoft VSS framework. Backup Agent does not use the Microsoft VSS framework. Consequently, Backup Agent does not participate in the backup when the VSS framework calls Pervasive PSQL VSS Writer and I/O operations are quiesced. Backup Agent must be separately added to the backup process. The backup process must also start and stop Backup Agent.