QSnap for the Image Level iDataAgent

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Overview

QSnap can be used with the Image Level iDataAgent to ensure that consistent backups can be taken from the active live system with the point-in-time snapshots created. Thus, all of the components necessary for basic Image Level iDataAgent functionality are available without requiring specialized hardware.

During an Image Level backup in a QSnap environment, the following sequence of events takes place:

The Image Level iDataAgent starts a backup operation.
On Windows, QSnap snaps the data to be backed up to free space on the source volume or another specified volume. On UNIX, QSnap copies modified data on the cache partition during the snap window. The cache partition can be linked for more information. (The cache partition cannot be on the same volume.)
The snapshot is backed up through the LAN.

Configuration

The following must be done before using the Image Level iDataAgent with QSnap:

Verify that the computer in which you wish to install the software satisfies System Requirements for the Image Level and File System iDataAgents.
Install the required software.
Review the Hardware and Software Considerations.
Setup the nOverrideVSSSnapSelection registry key to use QSnap for snapshot creation.

Required Software

For Oracle, the production server must have one of the following installed:

Oracle 9.2 Database (Enterprise or Standard edition), or
Oracle 10g Database (Enterprise or Standard edition)

Windows

The following must be installed on the production server:

Windows File System iDataAgent
Image Level iDataAgent
QSnap

QSnap is installed automatically during installation of the Image Level iDataAgent.

For a clustered environment, first install the Windows File System iDataAgent and QSnap on the physical nodes, and then reboot the nodes. After rebooting the nodes, install only the Image Level iDataAgent on the virtual node. (The Windows File System iDataAgent is automatically selected when you install the Image Level iDataAgent.)

Unix

The following software must be installed on the production server:

Unix File System iDataAgent
Image Level iDataAgent
Unix QSnap driver

For more information and procedures, see Deployment - Image Level iDataAgent.

Hardware and Software Considerations

Windows

When working with file systems other than NTFS, you must set an alternate COW Cache location on an NTFS volume. Increase the maximum size of the QSnap COW Cache to accommodate your disk configuration and usage. See Windows COW Cache for more information on COW Cache configuration.
After installation, it is highly recommended that you configure persistence for the volumes you are protecting. See Persistence for more information.

Snapshot creation depends on finding, within one minute, a 3-second period of inactivity on the volume being snapped. If the snap is unsuccessful during that one minute period, it must be retried. By default, the number of retry attempts is 3, after which the job is failed. For Image Level on Windows, to increase the chance of finding a suitable write-inactivity period, you can specify a greater number of retry attempts (up to a maximum of 10) by creating and configuring the nSnapRetry registry key.

Unix

The COW Cache mount point is selected at the time of installation. See Unix COW Cache in the Overview - QSnap page for more information on supported COW cache configurations.
When you add a volume to a subclient content, it is automatically configured as a CXBF device. See CXBF Devices in the Overview - QSnap page for more information.

If you encounter errors while configuring or deconfiguring CXBF devices on the client, go to /cvd.log on the client for more detailed information concerning the error.
If you apply an update to an AIX, Linux, or Solaris platform where CXBF drivers have been installed and CXBF devices have been configured, you must reboot the system after the update is applied in order to activate the CXBF drivers.
Use the Volume Explorer to deconfigure a CXBF device, deleting a subclient does not deconfigure CXBF devices for a client.
Raw volumes are not automatically configured as CXBF devices when added to the subclient content. Use the Volume Explorer to configure raw volumes as CXBF devices.

The Image Level iDataAgent for Solaris works with VxVM version 3.1 or higher.

Configure Extent Size

Unlike a File System iDataAgent, the Image Level Agent backs up extents on the source drive. The extent size is initially set to 512KB for Windows. The extent size can be configured to be larger than 4GB using the BackupExtSize and BackupExtSizeHigh registry keys. For Unix, the default extent size is 2MB (the Unix GUI will display 4096 because 4096 x 512 bytes equals 2MB). In most cases, the default extent size effectively divides the source volume and is best for performance.

But there may be reasons for increasing or decreasing extent size to improve performance. Keep in mind, for example, that a 512KB extent with just 10KB of data is backed up entirely, including its empty blocks of data. Again, this will work fine in most cases, but factors such as the state of data fragmentation on the source, network bandwidth, and server speed should be considered. These factors, along with extent size, can impact both the speed and the size of backups. These factors, along with extent size, can impact both the speed and the size of backups. If for some reasons the extent size is required to be changed, see Change extent size for Backup Applications for more information on changing extent sizes.

If performance is inhibited because of extent size issues, contact your software provider for more information about tuning your software for maximum performance.

Also consider the following implications of changing extent sizes:

Backup extent size must be uniform across source and destination computers.
In a clustered environment, all the physical nodes must have the same Backup extent size.
Backup extent size should not be larger than the size of the volume.

For Image Level on AIX, Linux or Solaris, the extent size can only be changed when the CXBF device is configured. Thus, to modify the extent size of an existing CXBF device, you must first deconfigure the CXBF device and then configure again.
When configuring a CXBF device from Volume Explorer for Image Level on Linux, the value entered must be a power of 2. Using a value which is not a power of 2 will cause the CXBF device configuration to fail. By default, the value is 4096; examples of acceptable values would be 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, etc.