QSnap for the Image Level ProxyHost iDataAgent

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Overview

The use of QSnap ensures that file system metadata remain unchanged, and therefore consistent, during the backup operation. QSnap is fully integrated with Image Level ProxyHost, creating a software snapshot during the Scan phase of the backup. Thus, all of the components necessary for basic Image Level iDataAgent functionality are available without requiring specialized hardware. For improved performance and flexibility, and enhanced features, you can supplement the Image Level ProxyHost iDataAgent and QSnap with a hardware-based snapshot implementation.

Configuration

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

Verify that the computer in which you wish to install the software satisfies System Requirements for the Image Level ProxyHost and File System iDataAgents.
Install the required software.
Review the Hardware and Software Considerations.
Configure subclient(s) and content. See Subclients - SAN iDataAgents for more information.
Create PreScan and PostBackup batch files. It is important to note that these batch files will have to be customized for each individual environment.
It is not necessary to quiesce the server for a file system backup with Image Level ProxyHost, and thus, no need of calling CVSnaptool from a pre-scan batch file.

We recommend that you test batch files before associating them with any subclients.

For specific information on the PreScan and PostBackup processes, see the Resource Pack for sample batch files.

Required Software

Windows

The following must be installed on the production server:

Windows File System iDataAgent
Image Level iDataAgent
Image Level ProxyHost iDataAgent
QSnap

The following must be installed on the backup host:

Windows File System iDataAgent
Image Level iDataAgent
QSnap

QSnap is installed automatically during installation of the Image Level (or Image Level ProxyHost) 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 the Image Level ProxyHost iDataAgent and the Image Level iDataAgent on the virtual node. (The Windows File System iDataAgent is automatically selected when you install the Image Level iDataAgent.)
All configuration for QSnap needs to be done only on the host machine’s Image Level iDataAgent.

Unix

The following software must be installed on the production server:

Unix File System iDataAgent
Image Level iDataAgent
Image Level ProxyHost iDataAgent
Unix QSnap driver

The following must be installed on the backup host:

Unix File System iDataAgent
Image Level iDataAgent
QSnap

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

Hardware and Software Considerations

General

Verify that the backup host is properly configured and connected to the S-Vol.

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.

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.

Configure Extent Size

Unlike a File System iDataAgent, the Image Level ProxyHost Agent backs up extents on the source drive. The extent size is initially set to 512KB for Windows. 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. 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 ProxyHost on 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 ProxyHost 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.